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August 1, 2001
6 Min Read
Editor's note: Consultant Bill Tobin of WJT Assoc. is a regular contributor to IMM and offers these tips for improving the efficiency of mold changeovers.
Too many people are whining about the exodus of jobs going offshore. Face it: If computers are being built in Hong Kong, nobody is going to mold in Illinois and ship to the Far East.
However, many industries are not moving because there is no reason to. Automotive will always manufacture near its consumers. Medical needs to be near its R&D facilities. Many telecommunications firms are watching products come and go so swiftly that being far away from high-tech designers is a waste of time. Thus manufacturing and molding are still stateside. The list is endless. Is there enough work for everyone? Sure.
Are there some buyers who still think they can have consistent supply lines from China? Yes, but ask the guy who took your business and shipped it to Pakistan how he intends to manage mandatory JIT production schedules. How will he administer an engineering change? How will he handle a reject? And lastly, what if U.S. policy changes and all of a sudden you can't trade with China or some other country?
Part of your competitive edge is going to be how well and at what price you deliver product. Your costs are based on material (over which you have no control), your efficiency (this means 1000 lb of plastic into the work order and 999.9 lb of good product shipped), your running time (24/7, fully automated, robots, and so forth), and your setup time. There are some tricks for faster setup times.
Heating the mold before it's hooked up will cut startup scrap by about 80 percent.
It is a common practice either to break out the changeover as a separate charge or bury it in the sales price. This is the machine rate multiplied by the number of hours it takes to hang the mold, start up the tool, pull the mold at the end of the run, and clean out the machine for the next job.
Here you need two things: First, do some quick research. How long (on average) do all things take? While I'll make no comments on machine rates, did you recover the cost of a changeover? If not, your first administrative change should be to remedy this situation immediately. If you are shipping on a JIT basis the assumption is that the mold is run each time you ship (whether you actually do this or not is none of your customer's business). The point is to charge for each setup you were supposed to do.
Secondly, think like a banker. Where could you invest to lower these costs? What would be the payback? How much would it cost?
Following are some tactics to help reduce startup costs and enhance paybacks.
1. Wherever possible install heated sprues or design your molds with hot runners. This shortens the cycle time, reduces regrind, and saves material. Return on investment: less than a month of running. If the client won't pay for it, heated sprues are removable. If the customer pulls the job, replace the conventional sprue bushing. Also, with some careful planning hot runner systems can be made interchangeable with other molds. Thus, when the job is done you have a usable system for the next one without the expense of a new purchase.
2. Even if this is at your expense, replumb all your molds and machines with manifolds, regardless of the size, so that there is one inlet and outlet for each half. In this manner you cannot hook the mold up incorrectly, you always have enough hose, and you never forget to turn on the water. Return on investment: about two to five production runs.
3. When I first started in this industry there was usually a gaylord on the floor feeding a huge hopper dryer sitting over the barrel. It looked like a summer camp ash tray you'd make in the craft cabin—dented, banged, and oily from being hit with the crane, pounded on when the material bridged, and other abuses. We'd draw straws for the poor sucker who had to climb up on a rickety, oily ladder/stairway to get to the dryer to repair or check it.
While such configurations are technically sound, they are geared for the automotive industry where material changes are few. When it comes to changing resin in such a system, time is wasted and material is lost by draining the hopper, cleaning it, loading it with new material, and then shutting down and drying the newly loaded material. Today, in the age of shorter runs and more frequent changes, we have portable material handling systems, which can save a ton of time during changeovers.
A portable material handling system uses a large (100- to 1000-lb capacity) hopper on roller wheels with a dryer, loader, and conveying system. The beauty of this is that the material can be dried before it's needed. A small 1- to 5-lb mini hopper/loader is attached to the feed throat to deliver resin to the press. To perform a changeout you simply disconnect the system, wheel it away, and install a new one. Return on investment: about 15 changeouts.
4. If you can follow the manifold concept, why can't you wheel the mold up on a cart, hook it up to a water source, and heat it before you hang it? Mold heating time can drop from 20 minutes to zero. Startup scrap generated is cut by about 80 percent. Return on investment: about one week of running.
5. If you run optically clear material or have highly controlled color matches you know how much time and material is put into the cleaning of the barrel. How much money do you throw down the drain "cleaning the barrel" by making bad parts? And, why are you doing it? Look at the money you lose compared to the cost of a separate screw and barrel combination dedicated to each material. Many machines have quick-change barrel hookups. While the cost may seem a bit high the return on investment is only a few months.
6. The old way to hang a mold is to bolt it to the platens. While there is nothing wrong with this strategy, if you must do it, give the setup team air wrenches with locked-down torque limiters. Bolts go in faster and more consistently. Also, take a look at quick-change systems on the market. Many are inexpensive, easy to use, safe, and are very low tech (meaning reliable).
Engel has one that aligns, centers, and clamps the mold in a matter of seconds. There are other good quick-change systems in the industry. Look for simple, robust, and easy-to-use systems. Spending a few thousand dollars on each machine to help get the mold install time down to less than 2 minutes has a very fast return on investment—usually less than a month.
I have a friend at a medium-sized molder (30 machines of all sizes) who in six months took mold setups down to an average of 15 minutes, with a maximum of 30 minutes on a 1200-ton machine. His goal is now to get it to 10 minutes.
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