Thread Before and After Plating (Part 2)

How to Control the Thread Size Before Plating?

As it is mentioned previously, the goal of OD control can be easily reached under stable CNC processing. Generally, after CNC processing, the threads of a non-plated component have to pass the thread gauge inspection so as to pass the QC inspection. Nevertheless, for components that need to undergo plating process, the manufacturing and inspection procedures will be different from the former. According to the requirement of our Swiss dental equipment supplier client, APPORO has to be discreet than ever for inspections. See the examples below:

Based on the required plating film thickness, APPORO has to leave some room for it during CNC processing, and use the pre-plated thread gauges for inspections. See the photo below. If the required plating film thickness is 1-3um, the major, pitch, and minor diameters should all be +0.02/-0mm larger than the standard dimensions when manufacturing the internal thread M13.2×0.3-6H. Then, the threads need to pass the inspections of the enlarged customized M13.2×0.3-6H +0.02/-0mm plug gauge before plating. After plating, the internal threads need to pass the inspections of a standard M13.2×0.3-6H plug gauge. Once they pass the inspection, they can be approved for shipment. If there is an external thread on the plated component, after CNC processing, the pre-plated ring gauge inspection will be necessary. And then, the inspection of a standard ring gauge should then be conducted.

 

What we can do without pre-plated gauges?

However, the customized pre-plated plug/ring gauges are all expensive, which are only needed for components that demand extremely high precision, but not for all components. With the long time CNC manufacturing experience, APPORO suggests to use NO GO of the standard thread gauge for the inspection criterion for threads before plating. That is, the threads could perfectly screw in the NO GO of the standard thread gauge without loosing. After plating, the threads have to pass the standard thread gauge inspections, a.k.a. GO and NO GO inspections.

This inspection is more available for components with plating film under 5um thickness. For components with plating film over 5um thickness, as its plating is for anti-corrosion purpose, and the precision requirement of it is usually lower. Even the ready made standard screws and nuts can be the inspection tools. Or, before plating the threads should be able to screw in the NO GO of the standard thread gauge but slightly loose. And then, the threads should pass the GO and NO GO inspections after plating.

 

When it comes to manufacture pre-plated thread, we have to leave some room for plating during CNC processing.
To use NO GO of the standard thread gauge for the inspection criterion for threads before plating. After plating, the threads have to pass the standard thread gauge inspections.

 

Plating and thread making are common techniques when speaking of CNC manufacturing components. Before and after different procedures, the concern will also be different. APPORO has devoted long time and and much efforts to CNC processing techniques, systematically learning from the processing experience in this field and turning it into application to increase the manufacturing efficiency and yield rates. Should you have any technical questions relevant to controlling size before/after plating, do not hesitate to contact us.

 

Learn more about thread gauge measurement:
Thread Gauge for instant measurement

Thread Cutting Tools Selection Guide

The definition of a thread is a spiral surrounded ridge structure with surrounding spirals in the round hole or outside of the cylinder. In terms of external threads, the peak of a thread ridge constitutes the major diameter, while the base of a thread ridge the minor. For internal threads, it is opposite. Besides, between major diameter and minor diameter, there is a pitch diameter, as known as an effective diameter whether it is an external thread or an internal thread. The purpose of the pitch diameter is to see if the thread could assemble with its matching thread successfully. If so, the distance between thread flanks will be equal. Because a pitch diameter is crucial to the assembly of the threaded parts, we generally use Three Wire Method or thread gauges for checkups.

Here, let’s discuss the common methods of producing internal and external threads respectively during CNC manufacturing process:

Internal Thread:

1.) Thread tapping

Usually refers to taper/second/bottoming three steps thread tapping. It uses a thread tap to cut the inner hole into an internal spiral surrounding the ridge. During the manufacturing process, cutting fluid has to be constantly filled in to lower down the temperature and to help residue removal. Applicable when the material is hard or brittle.

2.) Fluteless tapping

Compared with thread tapping which uses cutting to remove residue to process with the internal spiral, this method adopts thread tapping and then squeezes to form the internal spirals after drilling the pilot hole. Check out our previous case study for your reference. Applicable to the thread tapping of aluminum or brass made parts of which the threads are with better strength and stability.

3.) Internal threading tool

Identical to thread tapping that internal threading tool is also a method using cutting to process the thread. Internal threading tool has its advantage that it is able to maximize the effective thread hole depth of the blind hole. The limitation of the internal thread tool is that it is unable to process the threaded hole with too small inside diameter. Usually, it is recommended to use thread tapping for threads smaller than M5.

the tapping breaks in M2 blind hole of the aluminum alloy component.
Due to the incomplete residue removal of thread tapping process, the tapping breaks in M2 blind hole of the aluminum alloy component. Using fluteless
tapping could be an alternative here.

 

External thread:

1.) Thread rolling

Using cold forging to shape the external threads, this method is applicable to ductile materials. Before forming, the outside diameter of the component needs to be processed into the pitch of the thread. After forming, thread will be complete, precise, cosmetic with high intensity. This forming theory also applies to outside diameter knurling. Take a look at APPORO’s previous case study.

2.) External threading tool

Using cutting to remove the residue to process the external spiral. Cutting fluid needs to be added to help lower down the temperature and remove residue. Applicable to ductile and brittle materials.

3.) External thread tapping die

A disc-shaped external thread cutting tool. To use the external thread tapping die, the outside diameter of the round bar material needs to be slightly smaller than the major diameter of the external thread tapping die. Also, chamfer at the end of the round bar material will help the process of the external threading die. Using external thread tapping die to produce threads is more efficient, precise, while the tapping die costs more and is more applicable to threads with smaller outside diameter and components shaped like bearing shafts.

Concerning that only with high intensity can threads pass the destructive test, thread rolling is adopted for forming process.
The low carbon steel component is a piece of demonstrative equipment for tensile force test. Concerning that only with high intensity can threads pass the destructive test, thread rolling is adopted for forming process.