Background

As per conventional practice in sheet metal manufacturing industry, manual inspection fixtures are used as follows:

• Component / assembly rests at few small mating surface patches with location features
• It is clamped manually at certain points.
• The location and size of holes is checked by passing provided pins.
• The edges are checked with feeler gauge with reference to matching profile at the fixture.
• The traceability and inspection reports (if at all) are manually ensured.
• The process is too slow to be in-line with mass production; usually it is done for initial proving, on sampling basis and for resolving quality disputes.

Requirement

With drive for achieving “World Class Quality” and for detecting and arresting any flaw at first appearance there is pressing need for automation of “in-line” inspection and its integration with Production Monitoring System, ERP and Manufacturing Automation Equipment. There are 4 approaches for implementing the same.

Approach 1: Augmentation of existing Inspection Fixtures with Control Logic

• Microswitch / Proximity switch sensing is provided under each passed pin, for component presence sensing and for sensing of clamping.
• A graphic LED panel shows all complying points
• Further a PLC may be added for reading / branding the component i/d
• It may also brand / damage faulty component
• It could communicate the Quality records to host computer / server or even on Cloud generating a statistical record of specific failure points

Limitations

• Oversize holes may pass off as OK
• Edge matching, wrinkles, thinning and tearing would still have to be manually recorded through HMI
• It is “Go/No-Go” checking and cannot generate any statistical measuring data for SQC or determination of Cp/Cpk

Approach 2: Augmentation of existing Inspection Fixtures with Gauging Functionality

• In process Gauging instrumentation and Data Acquisition function is integrated with Fixture
• Probes employing various technologies and precision levels may be used. E.g., LVDT, Strain Gauge based, Piezo, capacitive/inductive gap sensing.
• Clamping and measuring cycle may be automated for in-line use.
• Micron level precision may also be achieved.

Approach 3: Use of Laser Distance Measuring

• Number of Laser Distance Measuring Devices may be mounted in Inspection Windows of a Line.
• Some identified points may be measured in 1mm accuracy level as the production flows.
• Alternatively single Laser Distance Measuring device may be mounted on position controlled motion system whereby it could digitize the programmed contours.
• The motion system could also be an existing CNC Machine and it could be programmed to digitize profiles covering the features of interest. Enclosed video clipping illustrates use of such as device in conjunction with a CNC machine for scanning and replicating a sculpture.

Limitation

• Device measures in one axis only.
• It could be used for coarse measurement only.
• Usually it could only be used for alignment and setting up rather than inspection.
• Use of Laser Radar at BIW Line

Approach 4: Use of Robot based Scanners

• White Light / Blue Ray Scanners are mounted on two Robots on either side of Line
• Full surface scan is recorded
• Comparison of point cloud with CAD model generates visual reports in color fringes
• Teach-in method is used for inspection program generation
• Could also be complemented by Gap-Flushness checking device on Robots

Limitations

• Precision level is 0.05 to 0.1mm mm which may be good enough for sheet metal but not for metrology grade inspection.
• It primarily generates free form surface digitizing, the metrology report of geometrical elements with GD&T is entirely based on computation and post processing
• Edges, holes and bores ( in case of solid blocks ) cannot be faithfully measured.
• Thickness/Thinning determination may not be accurate enough.

Conclusion

A judicious mix of these approaches could be used depending on budget, precision level, technology and process requirement, as long as there is compatibility of overall data integration.

Certain Quality parameters pertaining to aesthetics, wrinkles and optical defects would still have to be manually entered in through HMI at various stations.

Traditionally Cold Stamping Dies have been mostly deploying the principles of holding, guiding, mechanical cam actuation, clearances and material flow and somehow so far they have remained isolated from inclusion of technologies like Servo-hydraulics, Piezo Actuators, Electronic Sensors, and Telemetry

Given that cost of electronics has become much lesser than cost of Die and there is all pervading availability of hardware and software for Internet Communication and Data Acquisition; there is enough reason for these features to find application in Stamping Dies in near future.

Requirement:

1. There are many variables in the forming process and need is felt for adaptive control within tool. Sheet Metal Assembly Lines have already started coming with adaptive control of Spot Welding gun electrode squeeze, welding current and counter for spots and number of assemblies made. Weld Lines of the future could have Light Radar or Optical digitizers for in-line Quality monitoring.
2. Speed on Automated production Lines is so much that by the time a flaw may get noticed (if at all) already hundreds of faulty components/assemblies may get rolled out.
3. In complex scenario of automotive OEM where many metal forming processes are outsourced, it becomes increasingly difficult to keep track and get credible data of tool use /abuse, quality trend and condition of suppliers’ Press.

Features to come:

1. Electronic sensors which measure (in-line) quality, monitor process parameters and variability
2. Actuators which adapt to variations and automatically take care of requirements where same tool might be used for different materials or even for producing variants of similar component.
3. Internet of Things ( IOT ) Communicator to log the acquired data on Cloud.
4. Mobile and Desktop based apps to show customized dashboard and trigger auto mailer/sms to concerned personnel.

Some Examples:

1. Hydraulic CAMs are available, their use enables design of compact Dies since driver unit could be conveniently placed and offers possibility of multiple CAM actuations with control on sequence, speed and force. It could be readily integrated with Servo-hydraulic Control for adaptive control.
2. Gas Springs are used to substitute use of Cushion pins, traditionally all similar Gas springs were being charged to same pressure / force and they were connected together in parallel with common inlet, so that if any Gas spring leaked all would drop out of function together avoiding damaging skewed force at the Die. Now Gas Springs come with wireless communication of pressure reading to a host computer so that the forces could be individually set and monitored dynamically; this offers simpler reversible option for Die proving and tryout.
3. MATRICI Spain in its venture of High Tech Die ( HTD ) intends to offer following new integral service to its customers:
   1. Control the usage of the dies within the optimum conditions under which they were sensors that allow to check the main stoppage causes in real time owing to:
      1. Impaired Scrap sheds detection through sensor at Die
      2. Abnormal Kinematic detection through extensometer at Die
      3. Material splits detection by noise sensor
   2. Control and reduce the causes of production stoppage at the press lines by using designed:
      1. Measurement of Local and total stresses
      2. Production rate – Life Monitoring

HTD considers the following stages:

And also proposes the following solution:

The cycle time of a component is 6 min/part one expects 70 parts in 7 hours (one shift). Do we actually get 70 good parts in every shift? This question if asked to most production engineer, the answer is no and the number maybe anywhere between 50 and 70. Why is this so? The reasons are many, and can be classified under three heads.

• Availability
• Performance
• Quality

Availability or Availability Efficiency (Ae) is defined as to what extent is asset (machine, equipment) available for production.

Performance or Performance Efficiency (Pe ) is defined as to what extent is asset performance compared to rated performance.

Quality or Quality Efficiency (Qe) is defined as to what extent quality is produced as compared to rated quality.

Please note the words rated in italics in the definitions to which we will return a little later.

Availability

The formula for calculating Availability (Ae) is Available Time/ Loading Time where Available Time is (Loading Time – Down Time). Here Loading Time is the time in a day/ shift after accounting for breaks granted by the management, for example, lunch and tea breaks or personal time. Illustrating this with an example, in a day of 24 hours, if 30 min is provided for lunch/ dinner break and two tea breaks of 15 min each in each shift, the Loading Time would be 24 – 1.5 (lunch breaks in 3 shifts) – 1.5 (tea breaks in 3 shifts) would be 21 hrs. Now during the day there is a set up change of 60 min and maintenance of 30 min, then the Down Time is 1.5 hrs and the Availability (Ae) is (21-1.5)/21 = 92.85% or 93%

Down Time could be due to many reasons including set up change time, breakdown maintenance time, preventive maintenance time, chip removal time, coolant change time, tool change time, time lost due to no power or no tool or no operator or no work, time lost as machine is stopped for inspection or process problem or fixture problem, time lost due to new part development and so on. All time lost due to machine stoppage exceeding 10 min is captured under Down Time and affects Ae.

If in any company Ae is below 90%, one can drill down various Down Times, carry out a Pareto Analysis and determine which ones contribute to 80% of Down Time and then work to reduce them. For example if Set up time is a major contributor, one can use SMED principles to reduce it. If breakdown maintenance is a key contributor then autonomous maintenance is an approach to reduce it. Thus an action plan can be prepared to attack the Down Time after a thorough Why Why analysis.

Performance

The formula for Performance Efficiency (Pe) is (Parts produced * Actual cycle time)/ Available Time. Referring to our earlier example, against the expected 70 parts only 65 parts were actually produced in the 7 hr shift. Let us assume that there was no Down Time in this shift. In this case the cycle time is 6 min per part and the Pe would be 65*6/420 = 92.85% or 93%.

To analyse Performance Efficiency better it can be broken down further into two factors i.e. idle or minor loss and speed loss. Speed loss is the ratio of rated cycle time/actual cycle time. It is a measure to determine to what extent a process has deteriorated from its rated condition or ideal condition. The ideal condition is when everything is ideal, i.e. machine is new, raw material has the correct composition and machining allowance, cutting tools are sharp, operators are skilled in using the machine and well trained, and process is optimized. Production is lost if these ideal condition is lost. Even if the rated cycle time is maintained there are minor stoppages for example, an insert has to be indexed, a tool offset has to be given, a chip has to be removed during part loading, etc. Each of these stoppages are below 10 min and are not accounted in Ae but in Pe. Idle or minor loss formula is Parts produced*rated cycle time/ Available Time. Pe can now be rewritten as Pe = Idle loss*speed loss = (Parts produced*rated cycle time/ Available Time)*(rated cycle time/actual cycle time)

Performance is reduced for various reasons leading to less parts produced due to frequent change in process, long inspection time during which machine is idling, cleaning time, fetching tools or fixtures or material from another location, unoptimised part clamping/ unclamping time, inconsistent incoming material, variable manual operation time, low cutting parameters due to wear and tear of machine and many more reasons. The lost time is less than 10 min for each occurrence else it would be accounted in Ae. If Pe, Speed Loss and idle or minor loss is found less than 90%. one can drill down various losses, carry out a Pareto Analysis and determine which ones contribute to 80% and then work to reduce them.

Quality

The formula for Quality Efficiency (Qe) is (total parts produced – non confirming parts)/ total parts produced. Continuing with the earlier illustration if 3 parts were non confirming i.e. including scrap and rework, then the Qe = (65-3)/ 65 = 95.38% or 95%

The most important reasons for a low Qe would be lack of process capability. This leads to scrap as well as rework. Often this is a result of lack of control of inputs such as material, tools, fixtures, machine and process. Poor maintenance of machine can also lead to a lower Qe.

The Overall Equipment Effectiveness or OEE is a product of the three factors: Ae * Pe * Qe. In our example it would be 93%*93%*95% = 82%. This clearly shows that when manufacturing engineers talk about efficiency and quote figures of 85 to 90% in reality they may not be achieving it as it could be Ae or Pe or Qe alone and not the product.

One must have noted that both in Pe and Qe, we are considering the rated or ideal condition, i.e. the rated cycle time and rated conformance in quality (100% conformance to quality standards).

For an owner of a company, there is cost of money. This is the interest paid to a bank or financial institution on borrowing money, or the interest a promoter would earn if he were to invest his capital somewhere else. In either case interest is calculated on the basis of 365 days*24 hours. Therefore OEE should ideally be calculated on the same basis, i.e. 365 days*24 hours. In our example we calculated Loading Time as 24hrs less breaks allowed by management and arrived at 21 hrs. If one were not to do so and take 24 hrs itself as Loading Time, one would get a more correct picture of utilizing ones equipment effectively. The loss of 3 hrs is a Management Loss because management is unable to utilize the equipment during breaks. This is captured by a metric Me.

Total Effective Equipment Performance (TEEP) which is a product of Me*Ae*Pe*Qe. In this case Me is Loading Time/ 24hrs. In our example it would have been 21/24 = 87%. Now if OEE was 82% the TEEP would be 87%*82% = 71%. This shows that there is a potential capacity to improve productivity by as much as 29%.

The National Productivity Summit 2015 at Gurgaon on 20 -21^st Nov, showcases through its case studies and keynote addresses how teams have significantly improved productivity at their workplace. Various tools have been effectively used by these teams to discover the hidden losses in their process and they have found innovative solutions to their challenges thrown to them by their customers. This “out of the box” thinking is very important for these companies to continue to be competitive. Participants attending this summit can take away lessons and get motivated to emulate the award winners in their own companies.

This figure shows a TEEP of 41%, which is typical of many companies who start measuring OEE

Optimising Metal Working Process

Combination tooling: This is a favourite approach of many companies in large volume production. Combination tools certainly lead to cycle time reduction on VMCs and HMCs. There are a few problems that arise. Cutting speed is compromised to increase the tool life of that tool which has the shortest tool life. All tools do not wear the same amount at the same time. This is an issue especially in solid carbide tools while resharpening. Chips from one tool can clog into an adjoining tool. Since cutting parameters cannot be optimized for all the tools, chip breaking can be an issue. Spindle Power increases and the same needs to be checked. Roughing with a combination tool is acceptable but not finishing because the finish is affected when another cutting edge leaves or enters a cut.

Introducing LCA: LCA or Low Cost Automation aids are often used to improve productivity especially where assembly operations are concerned. Certainly this boosts productivity and motivates the workmen. Another advantage is that this knowhow is retained in-house. To design LCAs needs investment in training of personnel. It needs a strong 5S, Kaizen and enabling culture in the organization.

Optimising the cutting tool and parameters: Selection of the correct cutting tool and optimizing the cutting parameters is crucial to reducing cycle time and increasing tool life. Companies have invested in higher cost tooling and using higher cutting parameters and reduced the per piece cost because of higher utilization of the power and capacity of the machine and reducing the cycle time. Monitoring the spindle load and ensuring that it is optimally utilized is an approach used by many companies. This approach needs strong data collection to validate the results and periodic monitoring.

Using CAM programming: Companies have also studied the tool path and reduced the air cutting travel, thereby the spindle is cutting metal rater than cutting air. Sometimes due to lack of discipline and special causes that take place manual changes are made in the program and optimized cycle times are diluted.

Improved Fixtures and use of Accessories: Some companies have taken the approach of redesigning fixtures to accommodate family of parts. Others have modified fixtures to reduce setups. Some others have added 4^th Axis or additional axis on their machine to reduce multiple clamping and setups.

Deburring: Deburring is a troublesome process in most companies. Several approaches have been used including developing special tools to deburr on the CNC machine itself, to using different media to deburr. This needs extensive trials to validate the process including customer acceptance.

Use of DOE and ANOVA: For optimizing cutting parameters Companies have used ANOVA and DOE extensively with encouraging results. This however needs good in-house understanding of the process variables and the technique.

Better Asset Utilization

Utilisation of Generator Sets: Due to power outages in our country Companies have had to use in-house generated power. In most cases where the machine shop is large, several generators feed into a grid. An IT based solution has helped companies to optimally use generators based on variable load.

Reducing power consumption: Most machines have several motors for auxiliary functions, eg. coolant pump, chip conveyor, hydraulic power pack, etc. An innovative approach was to replace these motors by mechanical linkage driven by the main motor and thereby reduce power consumption. This approach may not work in all applications but companies have used one motor between two machines, eg. one coolant pump between two machines. The only problem is if the pump fails both machines would stop at the same time.

Refurbishing and upgradation of old machines: Reconditioning of old machines is an old story. In some cases especially in very large sized old machines, which are mechanically very robust Companies have not only refurbished but considerably upgraded them with latest features. While this works where the company is competent to carry out the work and the cost of a new machine is extremely high, it may not be advisable in many cases as technology has evolved and this would just lead to a compromise solution.

Design standardization: This is a route several companies have taken to improve the productivity in their design department where resources are generally a constraint. This approach needs a disciplined and a system based culture in the organisation.

Nesting: Improved nesting in powder coating, painting and heat treatment processes has led to significant increase in asset utilization and therefore productivity. This needs a deep study to understand the effect of higher nesting and validation of results in the longer term.

Layout and flow improvement in machine shop and assembly: Several companies have used this approach to improve productivity. Line balancing is a challenge but can be overcome.

Minor and idling losses: Several companies have looked at minor and idling losses in their machine shop and assembly areas. Small reductions and elimination of these losses have resulted in a cumulative reduction which is quite significant.

Productivity through quality

Process variable optimization: Heat treatment distortions can be reduced by optimizing various parameters such as temperature, soaking time, quenching time etc. This is an approach some companies have adopted to reduce rejections on thin walled parts.

Poka Yoke: Poka Yoke is a common approach adopted by most companies for eliminating rejections. Innovative means are used with low cost sensors, reed switches, motion counters to eliminate rejections.

Dimension changes in drawings: Assembly rework can be considerably reduced by revising the nominal dimensions of mating parts in an assembly after stack up tolerance analysis. The machining process to maintain the nominal dimension was critically assessed. Simply increasing the tolerance is not the correct solution.

Part cleanliness: Component cleanliness is a major issue in several industries. Companies have approached this challenge innovatively by studying chip formation, chip breaker design, chip evacuation, process changes, etc. The approach is to ensure that machining chips do not remain in the part in the first place.

Repeatability of measuring equipment: Often one takes for granted the repeatability of a measuring instrument and looks for reasons elsewhere. Critically and periodically assessing repeatability of measuring instruments has helped some companies to improve quality and hence productivity.

Improper part handling: Companies have found that improved part handling leads to lower rework and rejections. Though this is not new, part design is tweaked from the point of view of ease of handling during the process.

Manufacturing system redesign

Single piece flow: Several companies have adopted single piece flow against batch production to boost productivity. While this certainly improves productivity and drastically reduces in-process inventory, line balancing and reliability of each equipment is very important. Besides reliability of each equipment, the MTTR for each equipment must be very low otherwise there is complete loss of production. There remains a challenge to convert batch processes like heat treatment, washing, etc to a single piece flow.

SPMs to CNC: In moving from SPMs to CNC, companies have overcome the challenge of frequent setup change over using SMED and thereby improved productivity. This needs a disciplined and planned infrastructure to be sustained. The need to do this arose from fluctuations in customer demand and frequent introduction to new products.

Holistic view of the process: While redesigning the manufacturing system, companies have taken a fresh look at the system. Companies have introduced single piece flow, cellular manufacturing, Kanban, SMED, LCAs and innumerable Kaizens. The resulting benefits are huge. Value stream mapping is a commonly used tool to uncover waste in the system. Factory layouts have completely changed as a result. To do this, the management must be forward looking, bold in taking decisions, and take counter measures in advance to foresee disruptions, which to some extent are inevitable at least in the initial phase

The National Productivity Summit 2015 at Gurgaon on 20 -21^st Nov, showcases through its case studies and keynote addresses how teams have significantly improved productivity at their workplace. Various tools have been effectively used by these teams to discover and analyse the hidden losses in their process and find innovative solutions to challenges thrown at them by their customers. This “out of the box” thinking is very important for these companies to continue to be competitive. Participants attending this summit can take away lessons and get motivated to emulate the award winners in their own companies.

Beginning of the last century was an era of traditional craftsmen. Products were costly as they were custom designed and manufactured. Often the middle class at that time could not afford it, e.g. the automobile was owned by noblemen or kings. On Dec 1st 1913, the world changed forever. Henry Ford¹ installed the first moving assembly line for the mass production of an entire automobile. His innovation reduced the time it took to build a car from more than 12 hours to two hours and 30 minutes.

Ford’s Model T, introduced in 1908, was simple, sturdy and relatively inexpensive–but not inexpensive enough for Ford, who was determined to build “motor car[s] for the great multitude.” (“When I’m through,” he said, “about everybody will have one.”) In order to lower the price of his cars, Ford figured, he would just have to find a way to build them more efficiently.

Ford had been trying to increase his factories’ productivity for years. The workers who built his Model N cars (the Model T’s predecessor) arranged the parts in a row on the floor, put the under-construction auto on skids and dragged it down the line as they worked. Later, the streamlining process grew more sophisticated. Ford broke the Model T’s assembly into 84 discrete steps, for example, and trained each of his workers to do just one. He also hired motion-study expert Frederick Taylor to make those jobs even more efficient.

Automation in manufacturing increased and in 1981 Yamazaki Mazak set up a fully unmanned factory at Oguchi, Japan, for machining of castings and components of machine tools. There was huge publicity in the mechanical engineering fraternity since this was the first “lights out” factory where every night the factory operates without lights as no workmen are present. These systems were very complex and maintaining them was not easy for everyone. Such systems are capital intensive and not justifiable in every situation. Small improvements are also not possible and process design disconnects from the workplace.

The pendulum, which swung from one end that of a skilled craftsman at the centre of the manufacturing process at the beginning of the century to a fully automated one with no craftsman, had now swung to the other end. It was soon realized in Japan that a combination of human skills and appropriate automation may be cost effective, easy to maintain and leading to a competitive scenario. In the 90s Toyota Production System, Just-in-time became the buzz word in manufacturing. An offshoot, Gemba Kaizen, which means small improvements at the workplace, brought the synergy of human skills and automation in the form of Low Cost Automation to the Japanese workplace. By definition Low Cost Automation (LCA) means any compact, cheap, simple but very effective manufacturing piece of equipment which is designed and assembled internally by a group of employees at the Gemba using Gemba wisdom.

The key words are cheap, simple, designed and assembled by a group and using Gemba wisdom. By cheap, one means the ROI (return on investment) should be less than a year. Simplicity (Simple) should be in operation, design, flexibility and maintenance. If the LCA is simple then as products change it can be modified, taken apart and reused. LCAs are designed and manufactured on shop floor and the user is actively involved at all stages from design till tryout. It is a group activity and uses the wisdom of the shop floor.

LCAs do not necessarily use hydraulics, electronics, etc. A simple gravity chute to transfer parts from one machine to another is a LCA. A LCA can very well be automatic transfer of information. A simple hand operated trolley using a screw mechanism to load/ unload a component made from left over plumbing parts and a lead screw and nut from an old lathe can become a LCA. Fig1.

In Fig1. The two workmen with the help of their supervisor built this loading mechanism using left over pipes and leadscrew from an old discarded lathe. Their joy in creating something is palpable. The cost was 1/10 of that of an electrical hoist that would have been used. 

Once an organization decides to implement LCA it usually sets up a LCA or Kaizen Group. Members of this group are drawn from the manufacturing personnel who are multiskilled. They are trained using training kits in areas such as pneumatics, logic, PLC, etc. They are exposed to different innovative mechanisms and toys are a wonderful way to educate them. LCA room can be prepared with toys, Kaizen sheets, One point lessons, failed LCAs, hand sketches of proposed LCAs, etc. Fig.2 shows how LCA projects are taken up in the organization.

It is important to note the role of management in LCA. The leadership of the LCA group lies within the group. They decide when to meet, what to do, what resources are required, periodic review etc. Management’s role is limited to deciding, which LCA projects should be taken up, providing resources including training and rewarding when the LCA project is complete and implemented. Management must not be involved during design, manufacture or implementation of LCA.

The need for LCAs arises from the Kaizen events organized by the company. LCAs are designed from rough sketches made at the workplace. Corporate design is too bureaucratic, nor has any priority for carrying out this additional work. Rough sketches can be modified quickly and frequently on the shop floor. It also results in speeding up the LCA as the beneficiary is an active team member and is keen to expedite the project.

Table 1 compares LCA with conventional automated systems. A very important point to be noted; the LCA contributes to competitiveness as the knowhow is retained in-house, whereas a vendor can offer a competitor similar products. Automation often fails because certain considerations are not taken into account. LCA is also a highly motivational tool. Group members take pride in what they have achieved.

Some aspects that need consideration

1. Safety of operator and equipment can never be neglected and is of prime importance.
2. Automation fails if input quality is inconsistent. While designing an automation system, the worst case scenario of input material must be considered. When the user is involved in design as in a LCA, he knows the worst case and will take it into account.
3. There is a tradeoff between flexibility required and cost. If one desires complete flexibility, it may make the automation equipment very complex, costly and difficult to maintain. Often 80:20 rule is applied. Let the automation take care of 80% of product mix.
4. Before doing automation, one must simplify the process and movements. This makes the automation simpler, cost effective and robust.
5. Power failure is an endemic problem in our country. Automation system design must be robust under this situation and a recovery process must be built in.
6. If the automation handles a family of parts, then ease of set up change must be considered.
7. Finally use of automation equipment needs training and the same should not be neglected.

In conclusion quoting an automation champion from Japan, Mr. Shuichi Yoshida, “Manufacturing Technology tends to get more complicated, expensive, impractical and grotesque as design engineers work far from Gemba (users)”

Any automation system must be selected based on its appropriateness. For example a fully automated system is an appropriate solution in a high volume bearing plant, and cannot be designed and implemented by shop floor personnel. Nor can the ROI be one year. However an automated part unloader with manual loading can be a LCA, and more appropriate in batch production at a Tier II automotive component manufacturer. Appropriate automation must be cost competitive based on scale of production. While the words Low Cost Automation catch ones attention, it is not a solution for all automation requirements. It is more meaningful to use Appropriate Automation, which includes LCA.

¹ Reproduced from http://www.history.com/

By: Gautam Doshi

As a production engineer some years ago, I used to find it always a difficult proposition to economically justify investment for automation. First of all I had to convince myself, with numbers, that the company would make money if investment was done in automation equipment. I present below some views, which may not strictly pass an examination by a finance person, but can be understood easily by production engineers. Certainly financial experts can also use it especially those who can look beyond just accounts and have a wider business perspective.

Typically the cost to company (CTC) of skilled workmen in the organised sector is as per table below.

One finds indirect costs are as much as direct costs especially in the organised sector. In most cases this indicative figure is exceeded. However for this article and the calculations therein, Rs. 9,000 will be used as CTC for a skilled workman.

If the company works all three shifts, annual cost of manning a machine (on a three shift basis) would be Rs. 3,24,000 (9,000 X 12 X 3). Suppose we are able to purchase equipment, where we do not need to man this machine, we could save the direct cost and maybe 50% of the indirect cost. Some indirect cost would anyway be incurred, for example personnel dept. or management costs. Thus the cost savings for unmanned machine in three shifts works out to Rs. 2, 43,000. This is revenue that would be incurred every year till the workmen are employed to man the machine. The interest and depreciation of a capital equipment is also a revenue cost. For example if one depreciates at the rate of 20% per year (ROI in 5 years) and pays a 10% interest, the revenue cost every year would be 30% of the capital invested. Therefore for every Rs. 100 invested in equipment the company incurs Rs. 30 as cost towards interest and depreciation. Now if one were to invest in an automation equipment costing Rs. 8, 01,000, the interest and depreciation on this would be Rs. 2, 43,000. We are revenue neutral by investing this amount since we save manning cost and capital expenditure of Rs. 8,01,000 for automation is justifiable. If one were to depreciate at 10%, i.e. the life of equipment is taken as ten years; one could even justify Rs. 16, 00,000. If one factors in interest on reducing balance, a higher amount could be further justified; however one need not get into such fine details at this stage. We also know that the annual wage cost of Rs. 2, 43,000 is not going to be constant over five years. It is actually going to increase over the years as wages and other costs rise; therefore even higher investments in automation can be justified.

Sometimes it is not possible to run a machine in unmanned situation; reasons could be many. Let us now look from the aspect of optimum utilisation of the equipment. To do this we must first look at how most companies utilise their machines. A typical machine utilisation chart looks as below and is based on an available time of 365 days X 24 hours.

The chart shows that during lunch/ tea breaks and when the workman uses personnel time the machine does not produce anything. However during this time cost continues to be incurred. This cost is the financial cost of interest and depreciation as well as wages and salary. Potentially if the machine were to operate during this period, there is a cost saving of 9% (lunch/ tea breaks 6% + worker inefficiency 3%) To convert this figure into monetary terms we need to calculate the machine hour cost rate. The table below shows a typical calculation of machine hour cost rate as well as the proportion of labour cost.

On a machine in which one has invested Rs. 10, 00, 000, one finds the machine hour cost rate works out to Rs. 158. The labour cost as a percentage of the machine hour cost rate is 35%, on the basis of an annual CTC of Rs. 3, 24,000. In case the machine cost was Rs. 50, 00, 000, the percentage reduces to 10% of a machine hour cost rate of Rs. 522. This explains why the organised sector will invest only in costlier machines and vend out whatever can be done on cheaper machines to the unorganised sector, where labour costs are lower.

While calculating the machine hour cost rate it is assumed that the machine operates on a three shift basis. To calculate the cost incurred (fixed cost) when the machine does not produce, we remove the cost of consumables from the machine hour cost rate. This works out to 77% and 74% for the 10 lac and 50 lac machines respectively. One can take it as 75% for calculation. Thus the fixed cost incurred annually by a company for not producing during lunch/ tea breaks and when the operator is absent for personal reasons works out to Rs. 93,425 (158 X 75% X 365 X 24 X 9%). As this is revenue cost, when capitalised it would work out to Rs. 3,11,418 (93,425÷30%). Thus an investment of Rs. 3,00,000 in appropriate automation on a Rs. 10 lac machine, to the extent of allowing the machine to operate unmanned during breaks could be justified without too much difficulty. On the Rs. 50 lac machine this works out to Rs. 10,28,862.

In practice the benefits are much more because we have not accounted for the opportunity loss of 9% in terms of loss of profits, faster delivery, better ability to match demand and supply due to market variations, etc.

In conclusion, investment in appropriate automation may be justified on two counts; firstly in terms of savings in labour cost and secondly on account of using the equipment during breaks. There is however a third and very large area, which is not considered. If one refers to the pie chart on machine utilisation this accounts for 25% of available time and consists of weekly off, paid holidays and public holidays. During these days all financial costs are incurred, but without any returns. To mitigate this loss to a certain account, many companies carry out preventive maintenance during this period. Smaller CNC shops in unorganised sectors use extra workmen or incur overtime and try to utilise the machine during these days. Of course further automation could be thought of to use machines during these periods totally unmanned. However such solutions are very complex and often there are issues of reliability. Totally unmanned operation needs a very high degree of planning and very high consistency of inputs in terms of material and infrastructure (power failures are not acceptable). Probably such high levels are difficult to sustain in the Indian context and not appropriate even economically.

By: Gautam Doshi

Why does one purchase a machining centre? This question is best answered after studying the variety of components being manufactured in the machine shop. The simplest answer is when one has to do several operations, for example drilling, milling, tapping, reaming, boring on prismatic components; one can consider purchase of a machining centre. The advantages of machining centers are well known, however a quick recap is in order. Some advantages are unique to machining centers, whereas some are common to all CNC machines.

• Machining centers are flexible.
• Machining centers reduce set up changes because several operations can be performed in one set up.
• Machining centers result in better geometrical accuracy since related operations could be done in one clamping.
• Machining centers result in crashing of lead times because of reduced set-ups.
• Machining centers will lead to consistent quality.
• Machining centers will lead to consistent productivity.
• Machining centers deskill boring operations, which are otherwise operator dependent.
• Machining centers need fixtures only for holding and not guiding the tool. Thereby fixture cost and its maintenance is reduced.

While one can appreciate the advantages of CNC machines, one cannot overlook its disadvantages.

• Relatively high cost of investment as compared to conventional machines.
• Operating personnel need to be literate if not educated.
• Better shop floor planning and organisation to maintain uptime.
• Actual cutting times are the same as equivalent conventional machines, and as a matter of fact lower than that of multispindle special purpose machines.
• Maintenance of machining centers needs personnel with mechatronics training.
• High alertness of operating personnel. Since quality is consistent, a wrong setting or improper monitoring will lead to high levels of rejections and rework.
• Operational personnel need to be trained.

As in the case of CNC lathes, machining centers are advantageous where production requirements are batch type. For one piece production, except where complex contours are to be machined, machining centers are not likely to be economical. For large volume production as well, one could find special purpose machines (SPM) more economical. The reason stems from the fact that a machining centre is a generic machine not optimised for a specific component as a special purpose machine. Inspite of this, machining center are used in volume production. The reasons are several. To name a few, they include shorter deliveries as compared to SPM, ability to ramp up production, flexibility in case of product change, cellular manufacturing of a family of parts, etc. High sped machining centers in some cases can match the productivity of SPM.

Horizontal Vs. Vertical Machining Centres

One often faces a question, when should one select a Horizontal machining centre (HMC) against a Vertical one (VMC). The answer is quite simple - depending on the nature of components being processed. Box type prismatic components, with machining on multiple faces are more suitable to be machined on a HMC as against VMC. VMCs are most suitable for plate type parts where machining is predominantly on top and bottom faces. However HMC is a costlier machine as compared to a VMC. Therefore one has a via media solution of a VMC with an indexing head or with a 4^th axis. Please see accompanying flow chart, which includes rationale for selecting a machining centre as well as differentiating between selecting HMC and VMC.

Arriving at the machine specifications

Once having decided to purchase a VMC, VMC with 4^th axis or HMC, one studies the component drawings and writes a rough process sheet breaking down the total operations into face wise operations. This enables one to find out the total no. of cutting tools required on each face as well as those required to finish the component. This exercise must be repeated for all the components planned to go onto the machine and then consolidated. The smallest cutting tool used, its cutting speed and therefore its rpm will determine the maximum spindle rpm. No doubt this depends on the raw material to be machined. Machine tool manufacturers also provide information on maximum machining capacity for the specified power of the machine. For example the machine tool manufacturer will specify the maximum drilling capacity in steel, or tapping capacity in steel and cast iron, etc. This helps to select the spindle power as well as the maximum spindle speed required. One must also compare the weight of the heaviest cutting tool and its size with that of the limitations of the specific machine.

At the same time one also thinks about how the component will be clamped on the machine table – fixture requirement etc. Sometimes one wants to place multiple components on the table or multiple fixtures. This homework helps determine the work envelope required and therefore the table size of the machine as well as its strokes.

Flow chart for justifying/ selecting a machining centre & HMC vs. VMC

In the next part of this article, we will look at machine specification selection in detail.