EDM Impacts Cold Extrusion Die Manufacturing


EDM Impacts Cold Extrusion Die Manufacturing 
Form Grinding Relies on Wire and Sinker EDM Accuracy

Form Grinding wanted a better way to create the carbide inserts it used for cold extrusion forming in steel dies. The grinding wheel process they used to dimensionalize the carbide was slow and inefficient, and working with carbide on a grinding wheel is an untidy process. Plus it was costly, as the hardness of the carbide material wore out grinding wheels at an alarming rate.

The company creates tooling for the auto industry, which is about 99 percent of the volume of the Troy, Michigan operation. And, they needed to find a better solution for shaping the carbide in order to enhance process efficiency and throughput volume.

It was decided that Form Grinding needed to advance its technology by swapping out the grinding wheel machinery and by creating an entirely new pre-and post-forming process to help drive out operational costs. They purchased EDM machinery and used it to prepare the material on both sides of the cold forming operation, acquiring a U32 wire EDM and an Edge 2 RAM EDM from Makino.

They found that this decision eliminated much of the unclean environment of the grinding process, while at the same time it increased repeatability tolerances and product accuracy. They also now can order near-net part carbide with through-holes already drilled into them, which eliminates preparation steps for faster EDM production cycle times. It also gains them the benefit of unattended machining time during pre- and post-forming.

Carbide—Stronger Than Steel

Making tooling for fasteners on all parts of the automobile--including the steering column, the body, the engine block, the hood, the doors and the upholstery—is the market of Form Grinding. It is a $100 billion per year segment of the auto industry, though not as well known or practiced as the die/mold and stamping supply segments.

Mike Selimi, mill leader at Form Grinding, says carbide is used to form these bolts because it is harder than steel, which makes it an ideal match for the steel die/molds that are used. "Carbide is almost as hard as a diamond. And, it is impossible to cut with anything except a diamond. It can take the impact and pressure from the steel wire. And, the hotter it gets during the forming process, the more condensed and harder the carbide becomes to make the bolt.

"Cobalt and tungsten powder are baked to make the carbide bar, which is a clay like substance in its pre-processed state. Most machine shops and die/mold operations don’t like to deal with carbide because it is so tough to grind or work with. All you could do to prepare it for processing was to grind it with diamond grinding heads...and that is a dirty, dirty job as well as a costly and time intensive one. Multiple grinding wheels required constant changing due to the carbide hardness and material loss. And, despite proper ventilation, the dust problem was terrible."

Cold Forming

Depending on the job, four different stations may be used to cold form each bolt or fastener. Each station forms the part in various degrees toward final completion in stage four. The industry investigated standardizing the process in one step, but the carbide die is under so much pressure that it may cause the die to fail quickly.

"When they get hot, the carbide dies become stronger from the heat and pressure," says Selimi. "We’ve tried different products, and tried to get away from carbide. But, nothing else works the same. And you don’t hear a lot about cold forming because there are not many operations, as you have to heavily invest in a great deal of equipment to handle carbide for grinding and fixturing."

60 bolts/fasteners per second are created in most cold forming operations, and a die can produce up to 50,000 pieces. For the most part, Selimi says all the billions of bolts out there in the auto industry and many other markets are made through cold forming.

Many of the cold forming tool companies have been around for 50 years, and have been handling carbide pretty much the same way. Form Grinding and Selimi were determined to find another way.

The company discovered that they could pre-shape the carbide by a method other than grinding--through wire EDMing. Electricity was the only other process that could handle the tough carbide substance. Selimi notes the results have been fantastic.

"Our competition simply cannot compete. Where it will take them two weeks to complete a job run, we can do it in one day since we replaced grinding with EDMing."

EDM for Unattended Operations

Selimi says Form Grinding uses two EDM machines on both sides of the carbide forming process. The U32 wire EDM machine with a 12 pallet changing system, the only one like it in the US, is used first in the process.

"A .010" wire is typically used to prepare and form the carbide workpieces, which are 2 inches in overall length," says Selimi. "The U32K is user-friendly, and makes it so easy to prepare carbide, and is so much cleaner. Most importantly, the speed, accuracy and repeatability of the U32K relative to work piece production are fantastic.

"We can run 50 jobs overnight with unattended machining. Combined with the pallet system on the side, it runs without a hitch. It’s just very diverse, as there is no limit to what we can do on the machine to prepare carbide for processing. We can set up 12 inserts at 4:30 pm and they’re waiting for us the next morning. This allows us to provide competitive pricing, fast delivery and excellent quality."

"And the accuracy of the U32K allows us to order carbide with the through holes already drilled," says Selimi. "This saves us a lot of production cycle time and allows us to purchase carbide more cost effectively by buying in bulk.

"The finishes we are getting are unbelievable. We can achieve a 2- or a 2.5- micron finish in 3 passes, while this industry usually only asks for a 4-micron finish. And, we don’t even question the quality of the final carbide output anymore. We’re getting a little lazy, because the U32K is so easy to program and operate, and we know that it is right. The machine always holds size."

EDM for Bolt Processing

Once the carbide is prepared by wire EDM and it goes through the cold forming process, a RAM EDM is then used to add utility to the bolt. "If you look closely at a bolt, you will could see how the bolt has differing forms on it," says Selimi. "It has a shoulder and a head, which can never be formed in advance of processing. But, by using a RAM EDM, the carbide-produced bolt can then be put through a finishing process of shaping to create these features, which again replaces what grinding previously did.

"The Edge 2 RAM does not notice the difference in materials, as it cuts steel as easily as it cuts carbide. We only have to change the settings when going from carbide to steel, as programming and operations are similar. There is no difference. Due to the work that we do, which is small in volume and in size, we found the Edge 2 to be ideal. It allows us to handle about 90 percent of the cold forming work. And, it is accurate and user-friendly."

Selimi says that work done on the RAM EDM gives the head of the bolt its shape. "We used to get the hex bolt form by using six small, square inserts and grind them and work them to place inside of a ring to form that shape. Now we take a piece of carbide, which is put in that ring, and we rough it with the RAM to create the hex.

"The sinker (RAM) allows us to eliminate grinding the cylindrical bolts, and to process the heads on the hex bolts, which saves time," adds Selimi. "Plus, we’re able to get superior finish quality utilizing EDM technology, as we are able to produce a four micron finish using the Makino Edge 2." He also notes that the sinker is used for developing blind holes and other specialty work throughout the entire process.

Cold Forming Production Benefits

The major benefits for Form Grinding to add the EDM technology to their cold forming process has been cost and time. And, Selimi says these cost savings have been found in many areas.

They can now order carbide in bulk due to their quick turn-around time at Form Grinding. As carbide is tough to get, and there is a two to three week order period, they can now order more regularly and in advance, which saves on expenses and reduces cycle time. And the small holes needed for wire EDMing can already be put into the carbide purchased, saving further on set-up time.

Repeatability and accuracy in the process is very important due to high volume product, as is the ease of use of the machines. "The power settings on the machine are simple to change, especially compared to changing over grinding wheels for set up," says Selimi. "As the controls are the same on both Makino EDM machines, this also saves us time and money in training and set-up. And EDMing has eliminated the dust problem and the strenuous work problems common to carbide use and cold forming.

"You’ve got to hold size and be on top of your machine when grinding is part of the process. And, you can only have one guy running one machine and running one part. Utilizing EDM technology from Makino, I can run four different wires and three different sinkers all at the same time seven times faster than with manual grinding. We can do it overnight compared to in two weeks, and going from about 30 minutes to less than five minutes per cut makes good sense to me. We’re doing precision work but we’re turning the work around like its production work."

Form Grinding notes that this leads to another gain in unattended machining time. EDM technology also gives them the flexibility to engineer, alter and vent the dies as needed, which can relieve production pressure. And adding EDM machinery to the process allows Form Grinding to be ultra-competitive in their market niche, as they are able to cut prices to half of their competitors.

So why aren’t more cold formers moving to EDM technology? "People have been using sinkers for mold dies and wire for stamping dies for years," says Selimi. "But now the technology is finding a use in cold forming. Old time cold formers don’t like to switch to new processes until it is proven. At Form Grinding we have been willing to take the risk with the new process"

The Future of EDMing in Cold Forming

"We love the Makino wire and the sinker because they are able to cut and to work with anything," says Selimi. "We are not getting out of the grinding business yet, as we still have to grind forms in blind holes.

"EDMing simply gives us more flexibility with the making our carbide inserts for fasteners and bolts. When our customers now come into our shop, they know we’ve got everything that they need. We just have to change depths and set ups and the Makino EDM machines do all the work. Just to see them working as automated production and knowing we are getting unmatched precision for our customers is a great accomplishment."

"Makino has made the difference for us," says Selimi. "With the quality and performance of the EDM machines, the integration of a pallet system and the diversification of the EDM process, there is no limit to what we can do. Makino helped us engineer our system, trained the people on the operation and capabilities of the machines and helped us develop this new innovative process to drive out operational costs in our company and in our industry. There is no limit to what we can do with Makino."