Design Matters (Part 1) – Shrinkage

Shrinkage is a physical phenomenon mostly happening to molding parts made by plastic injection and die casting.
Shrinkage is a physical phenomenon mostly happening to molding parts.

It is always exciting to carry out new projects. However, before moving on to the production process, you have to make sure that your design already includes all the factors that might have influences on your parts. This time, APPORO would like to share with you how material shrinkage happens, and how it can affect your parts.

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Cross Knurling Profile DIN 82-RGV

Standard specification of DIN 82 (link)

 

After CNC fabrication processing, the workpiece is usually with smooth metal surface. Knurling is a manufacturing process to feature straight, crossed, angled, diamond-like lines or pattern onto the CNC components. Generally speaking, knurling can perform better grip for finger/hand operation, plastic injection insert or decoration purpose. Sometimes, we also machined multiple shallow slots or polygonal for same above purpose. DIN 82 is most commonly used knurling spec in CNC turning machining field. For example, DIN 82-RGV is with cross knurling pattern. DIN 82-RBR/RBL is with right/left hand spiral. DIN 82-RGE is with diamond-like 30° cross male knurling.

 

Failure Cross Knurling

Our Belgium textile industrial customer had sent us the original sample made of stainless steel 304. The sample made by Belgium local prototyping manufacturer was with failure knurling surface. See the shorter item in below photo. The measurement of sample was precise and within tolerance, but with bad knurling which was with improper length, too light pattern, and also lack of lead in chamfer at the threaded hole.

Cross Knurling DIN 82-RGV
Cross Knurling DIN 82-RGV Compare Zoom-in

 

The improper length of knurling do bad for its appearance, a customized full length cross knurling tool can solve this issue. Too light patter may result from the CNC programming or limitation of CNC lathe. Moreover, our CNC production lines can easily machine the lead in chamfer on the edge of threaded hole.

Improved knurling

Therefore, we ordered a customized full length knurling tool to meet the required pattern spec of DIN 82-RGV 0.8. An automatic Japaneses CNC turn-mill machine also helps improving the quality of surface and dimensions. Above photo shows the longer workpiece machined by APPORO is with improved knurling pattern.

 

We can offer CNC precision parts with several types of knurling surface, such like straight knurling, cross knurling, diamond-like knurling. Our production lines are also capable of knurling on precision plastics parts. Should you have any inquiry for above knuring surface on your CNC workpieces, kindly send us RFQ for free project reviewing without hesitation.

Aluminum Anodize Coating Failure

Aluminum anodizing is to produce oxide layer on the surface of aluminum parts to improve the capability of anti-corrosion. Actually, we had talked about this topic in previous case study. But, in this topic, we are talking about aluminum anodize coating failure. The failures caused by various issues on a aluminum CNC machining part generally fall into some of the following categories:

1.) exposure to chlorine based solution

Chlorine is very reactive and causes pitting corrosion by removing the oxide layer. Be careful if Chloride ion in a sulfuric acid electrolyte exceeding a critical level of chloride of 80 ppm. Please also notice that chlorine based solvents are for degreasing which may also cause acid pitting.

2.) exposure to very acid or alkaline solution

Solutions, pH lower than 4 or higher than 9, has the ability to break down the oxide layer and make the underlying aluminum susceptible to corrosion. Generally speaking, to rinse completely the aluminum anodize part is the most satisfactory method of eliminating this problem.

Blind holes v.s. anodizing failure

The anodizing failure rate can be high if your CNC aluminum parts featured with blind holes. If the high acidity anodization solution are not well removed from the blind holes, the liquid will flow out and damage the surface of CNC aluminum parts resulted in flaking-off and spots on its anodiizing surface.

 

Below photo showed an aluminum CNC milled part etched by acid residues. The white, dirty, flaking off oxide powder surrounding the threaded hole is gradually getting worse if no further action against it.

Aluminum anodize can be failure on occasion.
Aluminum anodize failure because of acid.

 

Preventive action to against failure of aluminum anodize

As described above, to rinse and clean the blind hole on a CNC aluminum anodize part is the best way to remove acid solution. It is a MUST to take this preventive action to against failure of anodizing.

 

Should you have any questions about aluminum anodize or other RFQ, feel free to send us RFQ for project reviewing.

Inner Thread Machining by Using Fluteless Tap

There are many ways for thread drilling in metalworking. As for external thread, both thread rolling and thread dies are most common used. As for inner thread machining, we generally use taper/second/bottoming three steps thread tapping or fluteless tapping.

Frankly speaking,  to drill a deep and small inner thread on high hardness or malleability raw material is a difficult mission. Thread machining is all about factors. Such as hole diameter, the forming speed and types of drill bet on the responses: torque, hardness, feeding rate, and thrust force of the form tapping process. Fluteless tap is the one of the best tooling for machining inner thread on CNC turning machines.

Fluteless tap thread machining
Thread machined by using fluteless tap

 

What is the Advantages of Fluteless Tap?

Fluteless tapping, so called form tapping. The screw thread is formed by plastic deformation of a working metal under high level of torque. And, well monitored operation processing to avoid tool bit breakage when thread machining.

Fluteless tapping can form a perfect screw thread with no waste material in a pre-drilled hole. Besides, it is kind of opposite style of external thread rolling method. The inner screw thread machined by fluteless tap is with higher strength and less error of pitch diameter. So, we mainly use fluteless tap machining inner thread on aluminum part, brass part and zinc part when in CNC precision manufacturing.

 

Thread Machining in Industrial Application

Let’s consider automobile industrial application as an example. Mechanical components need to have threaded parts allowing quick and precise assemblies and dis-assemblies. The engine heads manufactured with non-ferrous metals have a excellent capacity to deform and maintain an acceptable mechanical strength. As a result, thread formed by fluteless tapping can guarantee perfect full threading and high tensile strength.

 

Inner thread formed via fluteless tapping
Zoom in on the inner thread of cut part

 

However, inner thread machined by fluteless taps have some peculiarities. For example, the appearance of a split crest on the top of the thread. Above phenomenon is directly rely on the initial pre-drill hole diameter. In addition, the smaller the inner diameters, the slighter the split crest on the top of the screw thread after flutless tap forming.

 

the appearance of a split crest on the top of the thread
Split crest on the thread

 

Feel free to ask us if any questions about fluteless tap on CNC precision machining parts. Pls send us your RFQ for free project reviewing.