Current Status of Ultrasonic Precision Deburring of Plastics

Plastic precision moulding is a struggle against burrs!

Barrels, shots, etc. Customers who have tried everything.
For deburring plastics, try ultrasonic deburring cleaning.

Following the practical application of a system for removing foil burrs in the in-mould moulding of mobile phones, DVDs, etc., the Company has developed a deburring and cleaning system for precision plastic injection moulding, and has built up a track record of orders received.Recently, requests for post-moulding deburring of PPS have been increasing rapidly, and we have been busy with experiments and the resulting orders.

In the midst of this rapid economic downturn, we not only sell equipment, but also undertake commissioned ultrasonic deburring and cleaning work for customers whose production volumes are not stable or who have not yet received enough orders to purchase the equipment.We are now in the process of transforming ourselves from a manufacturer of powerful ultrasonic cleaning equipment into an ultrasonic deburring manufacturer that performs a wide range of ultrasonic deburring operations, from various metals and composite materials to plastic deburring.This paper summarises the current status of plastic ultrasonic deburring and its principles.

Current status of precision plastic deburring.

It is no exaggeration to say that precision moulding of plastics is a battle against burrs.The reality is that many parts of the deburring process are still not automated and rely on manual labour.However, even in China, where labour costs are relatively low, rising labour costs are inevitable, and many customers in Shenzhen and Dongyan are unable to recruit personnel for deburring, which is having an impact on their operations.

Deburring, which is a nerve-wracking but not skill-enhancing process, is another reason why it is disliked.The days of relying on cheap labour to remove burrs are coming to an end.

For example, at the Tianjin plant of a Taiwanese manufacturer of mobile phones, which employs one million people worldwide, it is said that 80% of the staff are even burr takers.

In a recent newspaper report, it was reported that immediately after the Lehman Shock, the management of the largest foreign-invested company in China deteriorated and the Chinese government provided huge support to prevent political instability [now recovered to more than before the Lehman Shock].I was concerned that this would further worsen the yield rate in the context of the development of precision machining, as quality control, as typified by deburring, was still dependent on low-paid manpower.

More than 100 people behind several injection moulding machines!of deburring workers lined up behind several injection moulding machines is not unusual.Rising labour costs are also inevitable in China.In-mould printing, which involves plastic injection moulding and printing at the same time, was a breakthrough in eliminating the painting process from the production line, improving the environment, shortening the process and providing beautifully printed products.However, foil burrs used for printing were produced, which could only be removed by hand and required a large number of deburring personnel.For this reason, mobile phone moulding and processing plants were built one after another in countries with low labour costs in order to reduce the labour costs of deburring.Hungary and Brazil are examples.However, this problem has been solved.This foil burr removal and cleaning system was successfully developed and put into practical use by the Company, and has been delivered continuously.However, the majority of plastic precision moulding is not in areas such as mobile phones, where surface beauty is a competitive issue, but mostly in moulded products where the mould burrs remain on the surface of the mould.However, even in China, where labour costs are relatively low, cost competition is increasing and reliance on people means that quality control is unstable.As precision processing advances, plastic moulding is also becoming more and more precise, and burrs are being debated as to whether they should be removed or not using a microscope with a magnification of 150x or more.There are fewer and fewer means of removal, and fewer and fewer burrs of a size that can be removed by hand.The market for precision plastic moulded parts is huge, far exceeding the market for in-mould moulding.The fact is that deburring of PPS, in particular, has had to be done manually due to its high pourability and excellent chemical resistance.There has been a worldwide demand for technology to remove the minute burrs that can occur even with these precision moulds.At last, we have succeeded in establishing and commercialising a technology for removing precision moulding burrs and processing burrs in precision plastics such as PPS, and we are now actively conducting tests, increasing the manufacturing capacity of our equipment and strengthening our sales.

Principle of ultrasonic deburring and cleaning

One example of fast-moving gases is gas explosions, but what moves fast during the creation and annihilation of microvacuum nuclei is a much denser liquid.The liquid moves at a speed of 50 to 100 metres per second (positive explosion) and then in the opposite direction at a speed of 50 to 150 metres per second (negative explosion).This is repeated more than 2000 times per second.Countless numbers of microvacuum nuclei are produced and annihilated synchronously.

The microvacuum nucleus group = cavity generated near the burr repeats on the burr, i.e. positive and negative impact forces, otherwise expressed as pushing and pulling, more than 2000 times per second.As a result, the micro burrs are instantly blown away.The burrs that are crushed and stuck to the body are subjected to more negative than positive, i.e. tensile, impact forces (some engineers still regard the mechanism of dirt removal by cavities as a unidirectional shock wave = micro-jet, which can only bite into the dirt).The dirt is gradually triggered and is destroyed (broken) and removed by similar repeated stresses.The rest of the process is similar to the precision cleaning process.

4800W Upper part of
vacuum-reduced ultrasonic deburring tank

2400W Deburring ultrasonic
oscillation Status Liquid surface

Deburring cavity Surface of
diaphragm Occurrence

Titanium nitride coated 2400W
deburring ultrasonic transducer

For deburring Cavity High-speed photo
1/1000th of a second

Titanium nitride coated 2400W deburring ultrasonic transducer for deburring Cavity High speed photo 1/1000th of a second An important aspect of ultrasonic deburring equipment is the ultrasonic transducer and cleaning tank.The ultrasonic transducer continuously generates powerful cavities, so that the diaphragm itself is continuously subjected to violent impacts.For this reason, the surface of the transducer is coated with 50µ hard chrome plating and a titanium nitride coating (see picture).Otherwise, the diaphragm will be destroyed by the cavities within a few months.Even more easily overlooked are the cleaning tanks.Like the object to be deburred, the cleaning tank is subjected to powerful cavity impacts.If subjected to a serious impact, even a cleaning tank made of SUS 304 3 mm can easily be destroyed from the welds.Therefore, it is necessary to design and manufacture safe ultrasonic cleaning tanks with precise control of cavitation so that there is no concentration of shock waves and cavitation in the tank.

[Points to bear in mind when carrying out ultrasonic deburring.]
When performing ultrasonic deburring cleaning, the ultrasonic frequency and oscillation system should be changed according to the size of the burrs, the location where they are attached and the shape of the object to be cleaned.The size of the ultrasonic transducer is changed according to the size of the object.If the impact force of the ultrasonic waves is too strong, erosion may occur on the surface of the object to be treated, resulting in the destruction of the mirror surface and, depending on the object, the destruction of the product.

To this end, the following measures have been taken

Changing the frequency of ultrasound

25KHz to 275KHz Simultaneous multiple-wave wide-area oscillation Deburring of complex solid geometries, PPS is at this frequency.
50KHz to 275KHZ Simultaneous multiple-wave wide-area oscillation Deburring of sensitive parts, electronic and composite components

Before deburringx100

After deburringx100 5min

Comparison with other means of ultrasonic deburring.

Comparison with the main other deburring methods.Ultrasonic deburring has many features not found elsewhere.

Any material.Various plastics, metals, ceramics, glass and their composites.Basically, most materials can be used, although there are degrees of difficulty.Rubber is also gradually undergoing technological development.
It is shape-independent, multi-directional where burrs occur, including tolerance holes on the inner surface.
Not limited in number.From one to tens of thousands can be processed at once or in series.
No hazardous substances, e.g. hazardous materials, are generated.Hazardous materials are not used.Use water.Hydrocarbon solvents if rust is a problem.Acids, alkalis and other solvents as required.Other solvents can also be used.
Burrs can be removed while cleaning without contaminating the cleaned material.Precision cleaning is possible.
No special technology or skills are required for use.Easy to automate.Easy to manage.
The main advantage is that micro burrs (micron size) can be removed more quickly and reliably.This is the only means available for future precision machining.
Even for delicate thin items [e.g. sheet materials] 50 µ or less in thickness, the technology has been solved by technical innovations.Masking technology is also important.
Development of combined deburring technology is also in progress.Ultrasonic electrolytic deburring technology is also being developed.It can be shared with other existing means of deburring.
Low consumables, e.g. filters.Small running costs.
The cost of the equipment is a matter of sales strategy, as it is unique, but in any case, as a system it is far less expensive than other competing methods that require precision ultrasonic cleaning after deburring.
Drying can also be done in line.Suitable for the treatment of precision parts processing air, as there is little re-adhesion of dirt.
The above-mentioned advantages mean that they can be installed in environments such as cleanrooms, which do not require isolated deburring and cleaning rooms, as other measures do, and reduce administrative costs.