Many times we receive a drawing with demanding tolerances, a 3D design that turn on all alarms, for example big accumulation of mass, with paralelism, perpendicularity or flatness in raw materials like polyamide with high percent of glass fiber. By this reason, we think it is necessary to bear in mind some considerations about design of injection molding based on more than 25 years of knowledge, that probably it could be of help.
In ZATEC we can advise to customer collaborating in this first phase of design, checking the feasibility analysis to optimize the design of piece, according to adequate raw material depending onf inal application and our process of injection molding, to reduce the investment if it is possible. As you can read as follow, we have remarked some examples about it:
although sometimes it is not possible to avoid changes of thickness, is very important to have homogeneus thickness without sudden cahnges always it will be possibe. An irregular thickness could generate problems like deformations due to differences of shrinkage in the mentioned thickness, or sink marks in the opposite face.
the sharp edges are stress concentrations (Kc) weakening the piece. Although we can do radii in some areas could complicate the mold, also we improve the design considerably. It is necessary to take acocunt the big accumulation of mass in the perimeter when we round this area. A good example is a plastic part like a box, and the barrel efect.
If we want a rigid piece, it is better to add nerves like reinforcement than increase the thickness. It is very important to bear in mind the crosses of nerves due to possible accumulation of mass, that as you know, this accumulation can generate asthetic defects. In areas with flat surfaces, besides of mentioned nerves, it is necessary to take account the cooling in mold with variations of temperatute, location and size of injection gate(s) and the chosen of adequate engineering plastic based on final application.
It should be designed to avoid big accumulation of mass, bubbles… theredore the important consideration is the difference between exterior radius and inner radius.
if it is possible, avoid the thread’s pitch too thin. In case of female thread, avoid the fillet ends up to final of piece by possible breaks. In case of male threads demolded by sliders, can be stopped at height of union line, avoiding if it is possible the problem of wear. As we have mentioned, is important to avoid the sharpd edges with weak mechanical properties, by this reason a good option is to reduce them.
The inserts must not weakening the around material, by this reason the optimum thickness of around material of insert, it must be verified. The shrinkage of plastic on the metal can generate an overflow. This overflow could be removed, doing a ribbed uniform and crossed in the insert part. Based on our knowledge, it is recommended to heat the insert before injectioning.
If we can help you with a project of plastic part, based on our expertise of engineering plastics and injection molding, do not hesitate to contact us like company of technical plastic injection located in Muel, Zaragoza (Spain), where we can collaborate actively with our customers.
It is not the firs time in Zatec where we found this phenomenom known like Creep, a problem to bear in mind depending on some final applications. Like injection molding company of technical parts in engineering plastics located in Zaragoza(Spain), we help to our customers to chose the adequate raw material based on final requierements. As you can read as follows, we are going to explain you this problem of Creep.
Sometimes, our plastic parts are subjected to constant strain during long time, and therefore, the deformation can increse up to break, even below the resistance of material. Normally, we represent in a graph with deformation or strain based on time, according to tensile tests. A datum to bear in mind is the Young Modulus, very usefull for designers due to we can include this mentioned datum in ecuations of resistance materials or simulations about finite element method by computer to predict the behaviour during lifetime.
The raw material, composition and, obviously, the process of injection molding can influence in their properties, like creep. For example, some materials with glass fiber have a better behaviour for this phenomenom than other unreinforced materials, due to hardness. In fact, the most materials used in Zatec have a lot of content of glass fiber, but this tipe of reinforcement could generate a fragile fracture. By this reason, we must consider some extra additives like impact modifiers or conditioning the humidity in some higroscopyc poliamides, avoiding or minimizing the mentioned fracture, being ductile fracture instead of fragile fracture.
The failure in plastic part could be by excessive deformation and due to formation of cracks. Therefore we will have a non-functional piece. The cracks can appear like an asnwer by applied stress, internal or external overcoming the intermolecular links like hydrogen or Van der Waals forces.
Some typical example is the break around of groves, where the final customer apply a force in screw due to tightening torque in the final assembly. Anyway the break could generates some time after.
Therefore, we can say like final conclusion, the creep is a combination of several factors that we must analyze before in the design phase to avoid the break by Creep.
Somtimes, we have received some quotations where a customer needs a flame retardant plastics, and/or with determinated homologated brand, due to several reasons. Nevertheless It is necessary to take account the type of flame retardant as you can see below, based on depeding on thickness.
An example, one request for quotation where we must us the homologated raw material “x”. But if we inject this thermoplastic we cannot meet the customer’s requirements due to the part had about 1,5 mm of thickness and the mentioned raw material was flame retardant grade V0 based on a test piece of about 3 mm of thickness. By these reasons, we consider necessary to talk about this additive used in several sectors like electronic, electrical or household appliances. We are talking about the flame retardant plastics.
According to UL94 classification (Underwriters Laboratory in EEUU, with their known yellow datasheets) and based on test where the test tube is burned in vertical by flame analyzing up to the fire is self-extinguishing. Therefore the different grades of flame retardant are as follow:
There are other nomenclatures such as 5VA, 5VB with vertical test tube, too. In these cases a burn can produce a hole or not. These cases are not so common than three mentioned nomenclatures before. The lower UL94 classification is for HB grade, where the sample is placed in horizontal. It is known like self-extinguished although this type burn like wood (to understand the simile).
Below you can see a good video from youtube (source:Filoalfa 3D) with different behaviours in final parts (ABS in this case), alhtought obviously there are more flame retardant engineering plastics like Polyamide (PA),Polycarbonate (PC)…
The flame retardant agentes more common to get some grades that we are talking about it are: antimony trioxide, red phosphor (common for dark colors), halogens (fluor, chlorine, bromine, iodine, astatine)… for example. But, sometime these elements can produce harmful smoke for human beings during combustion. By this reason each time is more usual to use flame retardants halogens free, from biological raw materials sustainably manufactured, decreasing the fossil resources besides of carbon emissions to atmosphere.
If you need technical support to chose the adequate enginnering plastic based on your application, we are glad to help you working together from initial design (bearing in mind our injection molding process) up to serial plastic part
Unfortunately, today is very difficult to talk without saying the word of COVID-19. Despiste of this, laying aside the santitary situation, where we do not pretend deepen now(although we understand this is the most important), but obviously we must to take a conscience of near future based on this eventually moment, due to automotive market has changed dramatically in few time, affecting to all supply chain, since OEM to final Tier-n company.
This year 2020 it already was complicated and strange. Zatec like injection molding company of technical parts in engineering plastics for automotive(mainly), we are seeing each day too many bad news about the stop in the manufacture industry in Spain, there is much uncertainty about the come back to the work in OEMs companies without a clear date. Anyway in ZATEC we will try to be optimistic, because we are looking to return with relative normality and with more force than before based on adequate safety measures, analyzing the current situation:
The pause in the production of several OEMs at national level(we can say global, in multinational companies), affecting to Tier1 companies, where the common is to cancel or postponed the ongoing orders, and therefore this situation generates more uncertainty increasing the “snow ball” kwnown like crisis, rolling down to the next companie in the supply chain. Logically, to avoid the quick spread of virus.
Almost all Tier1 companies have stopped their manufacturing process, many of them wihout previous advise, therefore there are several parts in transit wihout possibility to download up to new message or several orders in injection machines, but these parts cannot be sent. This is more stock, which we do not know what will be the date of delivery.
Talking about stocks, car dealers will decrease their sales. The reason is simple, the people will spend less money or spend the money in other things based on Maslow’s pyramide. Besides there is the battle betwwen electrical car versus Diesel cars, but this is not the adequate moment to open other debate.
All of this mix implies as follows, if the company does not invoice or the payment terms with their customers are very stifling, the companies will be problems with cash flow. Therefore this is an important value to take in count at this moment, and it would be necessary an action from government to promote this sector or others. As you know, everything is connected. By this reason, this mentioned action from government must be available first for Little and Medium companies, preserving the business fabric. The last crisis began wiht a financial collapse but now we think there is still margin to act.
Anyway, we already working thinking to return with a relative normal activity based on preventive safety plan. This is an oportunity to improve in all departments, adapting our work according to new situation.
We want to communicate you, the technical and sales areas continue at your disposal with a know-how of more than 25 years of expertise in injection molding, collaborating with customers since deign phase to serial plastic part.
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