Basics

You will have to examine your application and choose accordingly, but I will try to explain briefly some of the advantages to a hot runner solution. As I currently work for a hot runner company I see many parts that benefit from this application. Here are a few basic reasons to look into hot runners:

• Less waste -which in turn reduces contamination
• Controlled melt temperature - reduces warping of part as well as plastic degrading
• Great gate vestige - Reduces the need for second operations
• Lower injection pressures - allows for more cavities per mold
• Shorter cycle times - improves production efficiency

When using compression molding the cavity is slightly open when injecting and thus has more room for material. This way all the needed material can be injected rapidly into the cavity and instead of applying pressure in the material the mold clamps and thereby closes the cavity to the intended size (or volume). This reduces the internal stress in the part as you can image the molecules finding their own space so to say. Compression molding is very useful in thin wall parts to better be able to fill the part during injection and optical parts where stress will disturb the optical quality of the part, that's the pros.

However many beverage caps use continuous rotary compression molding which is altogether a different process. We used this process at a company I worked at for 35mm film cans and covers and it can be hypnotic to watch it run at full speed. If you look at a beverage cap and there is no indication of a gate mark on the part, it was most likely compression molded.

The injection molding machine outputs cannot be set, but the inputs can be each time you set the injection mold. Some of these set points, like mold temperature and barrel temperatures can be set. Of course this depends on which factors are the most critical to the injection molding process. If you had ability to perform a simple screening DOE before you put a specific injection mold into production, Minitab can pare to out the most significant inputs. If nothing else, these would be the ones to monitor. However, you'd likely want to capture fill time, cushion, screw recovery (loading time) and cycle time (especially if the machine is not run automatically.

Bottom line, if you have unlimited funds to purchase advanced monitoring systems and have employees that know how to operate them properly and analyze the data they produce, then by all means use them. But if you are dependent on your machine operators to produce good product, you must give them simple tools that they can understand and use while they are right at the injection molding machine. And they can monitor virtually every shot in real time, so if something does drift, or a machine or mold issue does arise, they can notify appropriate engineering personnel immediately.

Proper location of the gate point will be directly affect the quality of the injection molded parts gate location selection should follow the following principles:

1. Gate location should be chosen in parting surface, so that it would be easier for machining and maintenance.
2. The runner should be designed even, mold flow distance and sectional size in balance can achieved stable molding quality.
3. Gating location should be on the thick-wall area so it ensure the cavity can be filled completed.
4. The mold flow should not be right on the inserts or lifter, high pushing pressure of melt flow would probably deform the inserts.
5. Try to avoid weld marks or weld lines created in the critical surface, changing location of gating and try to make the weld line on uncritical surface.
6. Consider the venting when design the gating, make sure the end of the mold flow have good venting.
7. Gates should be easily removed and gate mark should not affect the appearance of the molded parts.

Injection molding is one of the most important processing methods to produce plastic parts. Plastic injection molding techniques have been used and developed for a long time. Look around you, the case of your laptop, the case of intelligent cell phone, water filters, food containers, wash machines and quite a few components in your car... yes, we are living in a world that are full with plastic parts, most of the common plastic parts are made by injection molding. This article will show you the basics of plastic injection molding advantages and disadvantages.

Injection Molding Basic Process
Feeding raw material from the hopper into the barrel, the plunger start to push, the plastic raw materials are pushed into a heating zone and then through the bypass shuttle, the molten plastic through the nozzle into the injection mold cavity, then water or oil run through the designed cooling system to cool down the injection mold to get a plastic article.

Soft tool is the tool made of pre-harden steel, it is an economic solution for a small volume production. It has advantages of low cost and fast turn around, but pre-harden steel is a lower grades steel that process lower hardness and wear resistance, so the soft tool can only stand molding cycles no more than 500k shots, it's also difficult to maintain tight tolerances.

Hard tool is a high quality tooling for mass production, it's made of the best quality steel, like H13,420 etc. Hard tool requires more procedure and longer time to manufacture.

Engineering plastic molded parts are made of engineering plastics, through injection molding process, the engineering plastics, such as ABS, PC, POM, are molded into parts with desired shape and measurement. Parts made of engineering plastics have better mechanical and thermal properties, it can be used as a replacement of metal in many applications, for example, plastic auto parts, medical parts, electronic parts, household parts etc.

Engineering plastic molded parts required firstly part design, then you need a mold making company to fabricate an injection mold, at the end, you need an injection molder to mold it. To achieve a good result, it is important to make sure that both the mold maker and molder understand the property of the engineering plastic. Unlike other ordinary plastic parts, the parts made of engineering plastic are supposed to be applicable on many aspects besides dimension or appearance; you need to do some test to make sure there are functional.

It's a common way to assemble plastic components or achieve functionality by creating hole features, Location and measurement of holes need to be carefully designed to minimize the complexity of mold manufacturing and negative influence to the part strength, in this article we are going to discuss what elements we should consider when doing rib design.

Quick link of the Troubleshooting Guide:

1) Dark brown spots 2) Brittle fracture 3) Bubbles (Or Steelyard balance : stranded gas) 4) Burn marks 5) Plastic injection molding machine of mucosa 6) Grain crack 7) Plastic degradation 8) Injection molded parts deforms 9) Injection molded cloak 10) Injection molded parts does not shrink 11) Surface roughness 12) Silver streak

13) Surface wrinkled skin texture 14) Color distribution 15) Fusion line location decline 16) Insufficient filling 17) Injection molded parts size differences 18) Systolic trace 19) Dirt marks 20) Sprue adhesion 21) Empty hole 22) Curved injection molded parts 23) Spraying trace 24) Surface layer (peeling)

Rib is a frequently used feature in plastic injection molded parts design for the purpose to enhance the strength of the plastic parts, typical rib design see below figure.

The thickness and location is essential of the rib design. Usually, ribs should be designed with a thickness of 1/2 of the wall thickness to avoid a thick section at the base of the wall, which would cause sink marks on the part surface. Ribs are usually spaced at a distance at least twice the wall thickness to allow enough steel between the ribs for adequate cooling.