Sponsored By
Bill Tobin

October 14, 2016

6 Min Read
Molding tricks for higher profits, part 2: The philosophy

Injection molding is a fully automated, high-volume process usually requiring thousands of parts at a minimum. If you want to do any activity, you need to “get your head in the game,” as coaches continually say in post-game interviews.

Start out thinking this way:

  • It is unacceptable to run anything less than full cavitation.

  • Filling all cavities at the same rate is mandatory.

  • There is no excuse for poorly functioning molds and equipment—preventive maintenance is always more profitable than repairing a breakdown.

  • Machines are always cheaper and more reliable than people. You'd be amazed what you can do with a sprue picker with a little creativity. Full automation inside the molding machine gives consistent cycles, higher yields and increased profits.

Image courtesy Todd Lappin/flickr.

Molding is all about profits. Asking a few innocent questions will point you to where you need to put your efforts. The technique is a Pareto chart: Look at all your jobs for the past few months. Draw up a chart showing what each purchase order really cost you (including the re-runs for rejects, etc.). Make a bar chart showing the actual profit per 1000 parts. Keep in mind that losing money on small jobs is still lost money, even if the large jobs make a high profit.

Applying the 80/20 Pareto principle works out to 80% of the money lost comes from 20% of the jobs. Now you know where to start looking!

Looking only at your “losers” makes up another Pareto chart. This time, as a group, find out where you're losing money:

  • Higher material costs you couldn't pass on to the customer.

  • Longer cycles you couldn't pass on to the customer.

  • Poor yields.

  • Molds or machines in need of maintenance.

  • Longer than budgeted setup/change-over times.

Let's look at each item.

Material costs. This is a cost you have no control over. Many buyers play the game of saying they only adjust the material cost once or twice a year. Each time you get a purchase order for parts, look at the current cost of resin. If the material cost is out of line with what you initially quoted, tell the buyer that you can't accept the PO without an adjustment to the current market price.

Longer cycles. If you've done everything in your power to improve the cycle time and you are still giving away all your profits, it's time to renegotiate. Contact the buyer and give him the new price before you accept the PO.

Expect a lot of screaming and yelling when negotiating prices on material costs and longer cycles, but look at the upside:

  1. You'll get some kind of a price increase because the buyer needs the parts.

  2. If the buyer says he'll pull the job, don't accept the PO and give him the mold immediately. This assumes you already have a “withdrawal policy” you submitted with your original quote requiring payment for excess resin, work in process, finished goods, custom packaging and so forth.

This is called “thinning the herd.” You hold on to the jobs that keep you in business and let someone else take the jobs where you're losing money.

Poor yields/molds or machines in need of maintenance. I've had many techs tell me "that mold doesn't like to run in this machine." This is usually a correct statement but it's an excuse for lack of, or poor, maintenance.

I had a client tell me to work on this. It shouldn't have happened. My client had a good maintenance program. The mold ran fine in any other machine. But in this machine the fill rate was unbalanced, a few cavities would produce occasional flash and several other cavities would show burn marks.

I looked at the machine history. Several months previously the machine had broken a tie rod. It was immediately replaced and (they thought) all was well. Tie rods cause the machine to build clamp pressure. They are actually springs. We jigged up some plate steel on the forks of a forklift, put a dial indicator on a magnet and shut the mold at full clamp and then measured each rod's stretch. Sure enough, the new rod stretched less than the ones that had several thousand hours on them. This meant one corner was seeing more pressure than the rest of the mold. A new mold with good parting line preload and deep run-outs from the vents had no problems running in this machine. This particular mold had minimal parting line shut off and the vent channels to atmosphere were deep enough. Uneven clamp pressure was causing all the problems

Several solutions were available:

  1. Ignore the problem and don't schedule this mold/machine combination.

  2. Try to adjust the tie rod tension—not practical. When you replace a tie rod, replace the entire set.

  3. Refurbish the mold.

My client chose the third option.

Maintenance must be almost an obsession if you want good productivity. The cost of maintenance is minimal compared to poor yields.

Longer than budgeted setup/change-over times. This is always a function of scheduling, tools and training. An idle machine or half-done setup is like a taxi sitting at the curb with a $500+/hour meter running, costing you in lost profits.

Mold change overs must be scheduled like a new job. Is the material available and already dried? Are the required people available (this might mean they eat lunch late)? Are the proper length knockout rods available and straight? Are the hoist rings semi-permanently attached to the mold so you don't have to hunt for them? Does the job require secondary equipment not normally available—welders, drills etc? Where are the packaging materials, instructions and setup sheets? Are all the cooling hoses available in the proper lengths so that you don’t have to make new ones?

Set up a video camera and film a mold change. How many times are people wandering around looking for a wrench, clamp, knockout rod or water line? Did someone leave to troubleshoot another machine, bringing the change over to a halt?

Analyze and train accordingly. With purging compounds, pre-dried materials, mini hoppers, portable dryers and mold-mounted cooling manifolds, you can be up and running with any machine less than 300 T in 45 minutes. Larger machines can be done in an hour. Super machines (1500+ T) can be done in two hours. This is what you strive for.

Look at your chart for the “bad actors” and respond accordingly. Look at your preventive maintenance program: Is it scheduled like any other job or is it on the get-around-to-it list? When you start solving the problems with the bad actors, you'll find what you've learned neatly leverages over to the rest of your operation.

With good maintenance, optimal yields, trained people and appropriate part pricing, even if the buyer threatens to pull the mold, you don't have to tell him how you operate.  The other guys with sloppy procedures will be losing money.  You only have to keep in touch with the buyer if you want to get the job back.

Bill Tobin is a consultant who teaches seminars and helps clients improve their productivity. He can be contacted at www.wjtassociates.com or [email protected].

Read part one of this series: "Molding tricks for higher profits: The expert syndrome."

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