Sheet Metal Stamping Machine Sheet

How to make a quality injection mold design and layout ?

Here is a story happened between us and one of our customers, Mr Rolando Matias Lopez from Argentin one year ago.
Mr Rolando Matias Lopez, an injection moulding enginner, and his colleague bought their former boss' plastic injection
moulding workshop,a small workshop equiped with only three injection moulding machines( 200T, 250T,350T), and they
only specialise in cable tie production for their customers in Argentina. He also told us that there are only three manufac-turers who specialise in cable tie manufacturing in Argintina, and he is one of them.

One year ago, Mr Rolando Matias Lopez wanted us to quote a new nylon cable tie injection mold for him.
Below are his product information and mold demand.

1. Product Name: Nylon cable tie
2. Product Material: PA66, made by DuPont ( Zytel® 101F NC010 )
3. Product Size: 180X4.8mm
    200X4.8mm
    225X4.8mm
4. Mold Demand
    4.1. To make only one injection mold with three interchageable cavities/cores.
    4.2. Cacity/Core No.: 1 X 40
    4.3. To make a fully hardened injection mold with more than one million shots lifespan.

　1. How he exchanges theese so small cavities/cores?
　For each mass production,such as for Type 180X4.8mm production, he has to exchange all the small cavities/cores of the three types. If his workers were accidentally to damage only " One Thread " in the cavity/core when they make assembly of the mold for each production,all the cavities/cores would be effected in some degress. He will have to close the gate in which the thread has been damaged,with the results that his production efficiency is decreased accordingly. If several threads were to be damaged, all the cavities/cores would be invalid, and this is the worst matter for his mold investment.
　No matter how his workers are carefull to exchange the small cavities/cores, the possibility of damage to them is still very high. Once only one thread in one cavity/core were to be damaged, his production would be effected in this way.

　2. A large injection mold with so many small cavity/core blocks that are sometions of no function is not a good solution.
　There is possibility of deformation of the small cavity/core blocks in mold long run production because these blocks are too small compared with the main cavity/core blocks.Once one small cavity/core block were to be deformed, there would be burrs on the cable ties in production, or the mold would not be even used any more.

　3. It is easy for the threads in the non-functional section of small cavity/core blocks to be damaged during production.
When in mass production, plastic or dust particles can stick to the threads that are not usefull for the time being, and then these particles can be slowly solidified on the threads, which will cause great damage to the threads.

Based on the above analysis and consideration, we decided to give up Mr Rolando Matias Lopez's mold layout and offer him a new layout solution to his mold design.
Below is the mold design and layout we made for him.

Mr Rolando Matias Lopez accepted our solution and believed that the mold design and layout we made for him is better for mold lifespan and mass production.

In his solution there is only 12 pieces cable tie tail small insert blocks, but in our solution, there are 24 pieces, double his, and also much bigger than his. Although we had to make more tial insert blocks and pay much more than what we quoted, we still used our solution. Now that the order for the mold had been placed and the first payment for it had also been made, we could not refer to a price increase of the mold.

And then, the mold construction began after his final approval of the mold design.

Mold precsion tooling video,
(1) Fast Speed CNC Tooling-Youtube:
(2) Slow Wire Cutter Tooling-Youtube:
(3) EDM Precision Tooling-Youtube:

After 45 days' working, we had finished the mold construction and started T1.

But when we made the first mold tiral, we met an unnexpected problem: the mold for 225 mm type could not reach a full
injection mouding ! At the four corners, the cable tie tails lack plastic material.

In fact, we had made moldflow analysis and thought that a full injection moulding would be no problem. But how this problem happened ? For the other type of 180mm and 200mm cable ties, there was no such a problem.

We tried different injection machines ( 280T,300T and 350T) and different brand PA66 ( Dupont, American Vydyne, and BASF),but it was no use. At last, we got an answer to this problem from a cable tie factory among our acquaintances " To add some liquidity additives to the PA66, such as 5%-10%, and then you can get a full injection moulding". " Each cable tie maker has his own secret formula, and this is a secret among cable tie manufacturers. You have never made cable tie and do not know about this." The acquaintance told us so. To be honest, we had never made cable ties and its injection mold before and also did not know this secret.

We made mold trial again according to this instruction, and soon we got a full injection for 225mm type at the third shot.
Mr Rolando Matias Lopez was very satisfied with the mold trial results. He confirmed the final samples as soon as he got them, and also made approval of the mold delivery quickly.

More than one month after he got the mold, Mr Rolando Matias Lopez complained to us that some Φ1.5 mm ejectors became curved after he ran the mold for more than 50,000 shots. He sent us a picture, showing us where the ejectors were curved.

In fact, the ejectors we used in the mold are high quality ones. They are made by JH, a famous Taiwan mold components manufacturer. Almost all the mold makers here use its ejectors for export plastic injection molds, including some big and famous mold maker. And its price is also three times as expensive as the same kind made by our local manufacturers. And so, we did not think that there was a problem in ejecotor materials.

We diagnosed what's wrong and found that we should have equiped the mold with ejectors with a little bigger segment at the curved point. The reason why the previous ejectors we used were curved is that the curved segment is so small, and not strong enough to hold a long strong pressure when the mold ran for a month.

Therefore, we asked him to change the previous ejector design,and sent him 40 pcs new ejectiors with a bigger segment free of charge.

Mr Rolando Matias Lopez was very happy with this. Ever since then, we have not heard about any bad news from him.

From the above case, we have at least extracted three items of experiences and lessons.

1. In mold making field, we cannot blindly follow a customer's requirements. If the requirements are reasonable and correct, we can follow them, but if his demand is unjustified from the view of injection mold tooling, we should advise the customer to correct it and take our advice. In the cable tie injection mold construction, if we had followed the customer's mold layout, he would have suffered mold investment loss after he had run the mold for more than 0.1 or 0.2 million shots.

2. Don't always worry about a loss you suffer. As an English proverb goes, "Suffering a loss is a blessing." In the above case, because of change of the mold layout, we had to pay more than what we quoted for the mold materials and tooling, but we did not ask for a price increase of the mold, which meant that we would earn less than what we quoted, suffering a loss in this. We also kept this situation informed of Mr Rolando Matias Lopez, and he told us we could offset such a loss in his future mold projects.

3. Good after-sale services should be provided in time. To track the status of customized export injection molds and injection molded plastic parts or products effectively and to communicate with related customers for any abnormal situation and take action to correct immediately. In the above case after we knew the curved ejectors, we sent Mr Rolando Matias Lopez 40 pcs Φ1.5 mm updated ejectors at one and he got them in one week. In this way, he avoided market loss.

This year, Mr Rolando Matias Lopez has also placed mold orders with us as he promised. One is for type 250/275/300mm X4.8mm,and the other is for type 350/390/430mm X4.8mm. And we have also finished the two molds very successfully.

All stories have an ending, better or worse, fascinating or common. We have got a good end in this story.
All's well that ends well, although its process is a little longer.
This is true in business, and also true in our lives.