In today’s environment of increased competitiveness, what is the secret to maintaining and increasing the profitability of your wire EDM equipment? The one thing that will help to increase the profitability of your wire machine is reliable wire threading. If you can increase the amount of time your machines can run without an operator then the cost per part will decrease significantly. The wire threading mechanism is the single most important component of your wire EDM operation with the exception of the operator. If you find yourself with less profit in your parts that are machined on your wire EDM equipment then read further. In this article we will discuss the costs associated with the operation of a wire EDM machine. We will review why your old wire EDM machine that is paid for may be costing you more than you realize. We will review the criteria that should be used in purchasing a new machine.
Before we can understand the premise proposed in this article we must first understand the costs we incur in machining with a wire EDM machine. These costs can be divided into two categories. The first category is the cost of actually running the machine. We will call this category “Fixed Machine Costs”. The basis for these cost are the expenses associated with having the machine eroding parts. The costs that must be considered are:
These costs will vary depending on your geographic location, machine manufacturer, and age of the machine. The cost of electricity will vary by geographic location; there is little you can do to reduce this cost without relocating your facility. The cost of wire and consumables will vary depending on both the manufacturer of your equipment and the age of that equipment. Some machines recommend that you use a coated wire to achieve maximum results which will have an effect on the cost of operation. This is not to say that this is a negative as this machine may perform better for your specific application. Other machines may require specific types of filters and resin which can also affect the cost of operation. Maintenance costs will be more for older equipment as it will require more time and parts to keep these machines in working order. In general these Fixed Machine Costs will average between $8 and $12 per hour. Many salesmen will tell you that the cost of operating there equipment is less than this and they may be able to make a convincing case for why this is so. As you will see this cost is relatively insignificant to the overall cost of running your equipment. The second category of costs is related to the operator of the equipment. We will call this category “Operator Cost”. Once again this category will vary by geographic location and the level of expertise required to produce you parts. The costs we must consider are:
The range of this category is wider as these costs will vary widely by geographic location and the level of benefits provide for your employees. The average cost for Operator Cost will be between $25 and $60 per hour. Please realize that just because you have a lower cost operator this does not necessarily relate directly to the cost of the parts produced. A less experienced operator may make a lower hourly wage but he may also cost you more in increased setup time and scrapped parts. The obvious conclusion from our assessment so far is that Operator Cost is by far the most important factor in calculating the overall cost of producing a part. We will continue to explore this relationship as the article progresses.
The premise of this argument is that you are machining parts that will benefit from unattended machining. It may be that you only manufacture parts that require a single shape for each part and it is not feasible to mount multiple parts on your machine. If this is the case then your operation does not fit within the parameters that we are using for our discussion. You may however can some insights into the actual cost of producing parts on you wire EDM machine. For those of you who produce parts that do fit our requirements then we will progress with the discussion of how to reduce your costs.
If you don’t think that wire threading is an important factor then consider the fact that almost all wire EDM machines produced to today come standard with a wire threader. This is an additional cost that manufacturers would not include if they felt it was unnecessary. Most machine builders have gone to great lengths to improve the reliability and speed of their wire threading mechanisms. We will discuss the requirements of wire threading for specific applications later. For now let’s assume that you want a reliable threader on your machine.
To illustrate the advantage of unattended machining we will use an example part which has six shapes with a length of 2.5 inches each and four .375 diameter dowel holes. For this example we will assume that the threading location for the six shapes is .125 away from the shape and the threading location for the dowel holes is at the center of the hole. This will make the actual roughing length of each of the 6 shapes 2.625 and the roughing length of the dowel holes will be 1.975. For simplicity our plate will be 1 inch thick. We will look at two machining scenarios. The first scenario will have the machine rough each shape and drop the slug with a traditional glue stop and then proceed to immediately take three skim cuts. The second scenario will have the machine rough each shape to within .05 of cutoff and then cut the wire and proceed through all of the shapes using the same method. After all of the roughing cuts have been processed the machine will then return to each opening and perform the cutoff to remove the slug. After all the slugs have been removed the machine will then return to each opening and perform three skim cuts. For this example we will assume that the wire threading time is two minutes. We will not consider the time it takes for the machine to position between shapes. We will also assume a roughing speed of 30 Sq/in per hour. For skim cuts we will use a factor of 1.25 times the roughing time to calculate the time it takes to perform the three shim cuts. We will also use a slug removal time of 5 minutes. All of these times will vary from machine to machine and you can adjust them accordingly for your equipment.
The total cycle time required for this example part will be 167 minutes and 3 seconds or 2.79 hours. If we use a Fixed Machine Costs of $10 per hour and an Operator Cost of $40 per hour we will have a total cost to operate the machine of $52 per hour. In this scenario the operator will have to be at the machine through the entire process. The total cost to produce this part will be $145.08.
The total cycle time required for this example part will be 213 minutes or 3.55 hours. The operator will only be required to be at the machine during the cutoff and slug removal phase of the program which will be for a total of 57 minutes and 12 second. The part cost now looks like this: 3.55 hours at $10/hour for $35.50 and .953 hours at $40/hour for $38.12. This brings the total cost to produce this part will be $73.62.
The cost to produce to the part in scenario two is nearly half of the cost in scenario one even though it took 46 minutes longer to cut the part. The reason for this savings is the reduction in time that the operator spent attending to the machine. You parts may involve larger or smaller shapes and different quantities but in almost all cases you parts will cost less to produce using scenario two. There are other methods of reducing operator time such as no-core machining where the slug is eroded totally eliminating the need for the operator. Obviously only small shapes can be machined using no-core as the additional cost involved with the increase cycle times quickly becomes prohibitive. However you should not overlook the possibility of combining no-core with traditional roughing where the slug is dropped during the first cut. Depending on the lengths of the shapes and their number it may be possible to do all of the roughing cuts on the larger shapes first while the operator is available and then to no-core the smaller shapes and do all of the skim cuts in unattended mode. This may require a rethinking of how you program and process your parts but it is well worth the effort. In addition to the cost savings you should also realize additional machine time as your machines should be able to now run a portion of many nights in unattended mode when no operator is available. This can postpone the need to purchase additional EDM equipment as you may gain as much as 30% in available machine time. If you choose to undertake this process it should be realized that your programmer will need to be capable of creating programs in a number of different techniques. The programmer may have to change programming methods based on changing schedules. With a modern CAD/CAM software package this should not be difficult.
You will notice that we did not include the cost of your monthly payment in our calculations. The reason for this is that this we are considering this a fixed overhead expense. You will make your machine payment whether the machine is running or not. In many cases if you own an older machine that has been paid for you will assume that your cost will be less since you no longer are making payments. This is not usually the case because many older machines do not have a wire threader or if they do, it does not function reliably. These machines are best utilized for jobs that don’t require cutting multiple shapes. If you use our cost calculation you will be shocked to see the difference in cost between an older machine and a new machine if wire threading is involved.
If you only have one machine can this process work for you? Of course it will, but only if you can utilize your operator in some other capacity when he is not attending to the machine. This may be in a programming capacity, inspection or operating other equipment. If you have multiple machines this will allow a single individual to operate more than one machine. Even though you may operate your machines in this fashion now if you are not programming for unattended machining you will probably find that many times one of your machines is sitting idle waiting for the operator.
Now that we understand how critical the wire threading mechanism is to our profitability we should consider maintenance. A wire threader is a mechanical device and to operate correctly and reliably it requires maintenance. It is easy to overlook the suggested maintenance on equipment because this is non-productive time when we are not cutting parts. This is a serious mistake as your wire threader will not work reliably without proper maintenance. That one hour per week required to maintain you threader will more than pay for itself in improved profitability. Another factor that is seldom considered in wire threading reliability is the wire itself. If you are purchasing wire strictly based on the cost then wire threading may be affected. The amount of curl in the wire as it comes off the spool is an important factor in threading reliability. Residue on the wire can also play havoc with the performance of the wire threading mechanism. Additional maintenance may be required if an excessive amount of residue is present on the wire. Once again the least expensive wire may not result in the lowest cost to produce a part.
With a firm understanding of how important wire threading is to our profitability we should make sure that we investigate this fully before purchasing new equipment. In most parts like our example the roughing speed of the machine is not going to significantly affect the cost of producing a part. A quick and reliable wire threader will be the most important feature of any new piece of wire EDM equipment. There are several things to consider when looking at wire threaders:
If you are considering purchasing a new machine I would suggest that an important test part for the machine would be one that requires multiple threads through different size start holes. Insist that you get a report on the total cycle time to complete the part and how many threads were missed. For a sample part feel free to send an e-mail to rmell@cam-1.com. Study the machines carefully and make sure that you have a full understanding of the threading mechanism. This seemingly minor component has the potential to affect your profitability more then anything else. Most all machines will come with a threader but this does not mean that they all have the same capabilities. Do your homework and make the smart choice for your needs.
About the Author
Randy Mell is the President of CAM-1. He has been involved in the programming of NC/CNC equipment since 1976. He has been involved in the wire EDM CAD/CAM business for the past 20 years. In addition to selling software he also does on-site training and class room training on Esprit SolidWire products and is available for consulting to help your EDM profitability. He has no association with any wire EDM manufacturer. He can be reached toll free at (877) 4 EDM CAM or via E-mail at rmell@cam-1.com.