Welding Processes for Plastics

 Welding processes for joining plastics are numerous – a selection is listed below.

 1. Laser Welding or Laser Beam Welding (LBW)

Also known as Laser Beam Welding (LBW) this welding technique is used to join pieces of thermoplastics using a laser. The laser beam delivers a concentrated heat source permitting narrow and deep welds with high welding rates whilst the two parts are put under pressure. Speed and precise control are two of its many benefits.

2. Ultrasonic Welding

Ultrasonic plastic welding is a commonly method that has been in use for a long time. It uses the heat generated from high-frequency mechanical motion to join thermoplastics. It happens by transforming high-frequency electrical energy into a high-frequency mechanical movement. You can use ultrasonic welding on almost all plastic material. It is known for being affordable, clean and meeting quality requirements.

3. Hot Gas Welding

A commonly used welding process for the manufacture of smaller items (heat exchangers, chemical and water tanks…), hot gas welding used a specially designed heat gun. The hot air that the gun generates softens the plastic parts to be welded and the plastic filler rod which needs to be of same or comparable plastic material. Also added to the weld joint in addition to the hot gas is a plastic filler material to aid the bonding process.

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4. Spin Welding

For the joining of plastic components, spin welding uses surface friction focussed in a circular weld joint. It produces the heat needed for the melting of the surfaces to be joined by spinning one of the parts relative to the other. The two parts are held under a controlled load. When the spinning stops the joint will be left to cool.

It can be used to weld plastic components of big sizes and is a fast process but one of the parts needed to be circular. One of its uses is the sealing of containers.

5. Vibration Welding

Vibration welding, also called linear or friction welding, is when two plastic pieces are connected under pressure. The heat is generated when a vibration is used along the common interface. Compared to hot plate welding, it is much faster and more accurate.

6. Hot Plate Welding

One of the oldest process, this is a thermal welding technique used for joining thermoplastics. In order to melt two surfaces, a heated metal plate is placed against or near and the surfaces are connected together under pressure. This method is simple and produces strong joints in most all thermoplastics so it is commonly used in the mass production or large structures such as plastic pipes of large diameter.

7. Friction Welding

Friction welding of thermoplastics is often employed for joining injection-moulded parts and was established some time ago. It uses friction to produce heat and to join two pieces together. Friction welding delivers many benefits to manufacturing and is often used in the aerospace and automotive industries this technique to join metals and plastics.

8. Frequency Welding

This plastics welding technique, also known as high-frequency welding or radio-frequency welding, uses electromagnetic field to join two plastic parts. The high-frequency electric fields are used to heat the material and pressure is also added to soften and join the two materials together resulting in a strong bond. Polyurethane and PVC are welded with this technique.

Where is it Used?

There are many types of plastic and it is a versatile material used in a wide range of sectors such as packaging, electronics, construction, fabrication, medical, aerospace, automotive and many other industries. When correctly applied, plastics welding can be enormously strong.

Some video:-

                                           

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Plastic part design Rules

Overview:- The following is a summary of the design rules covered in both Designing Injection Molded Parts and this course. Keep in mind that these rules are more or less guidelines intending to help you design parts that can be successfully molded. In extreme cases, it is possible to bend or even break some of these rules. You should consult a tool designer to determine the mold capabilities available for your design.

Wall Thickness:-

 - Maintain uniform wall thickness as much as possible.

- If you have not yet determined a material, a thickness of approximately 2.25 to 3 millimeters (.09 to .12 inches) is a good starting point.

- Typical wall thickness' based on material are outlined in this table. 

- When changing wall thickness, do so gradually over a distance of at least three times the change in thickness. Use a radius for a smooth transition.

- When changing the wall thickness, do not exceed 25%.

Draft:-

 - Always add draft to the walls of a part. Draft can be as small as 1/4 degree, but many materials require more.

- Add more draft to walls greater than 25 millimeters (1 inch) in depth.

- Add a minimum of 5 degrees for textured surfaces. Some texture may require more.

Undercuts:-

 - Add draft to undercut surfaces to easy operation of slides or lifters. 

- Plan for cosmetic blemishes formed by slides and lifters. 

Openings:- - Ensure there is a minimum of at .125mm, or .005in, for the contacting steel to pass for a shutoff opening. An angle of 3 degrees is preferable. 

Bosses:- 

- Add Draft to the inside and outside walls of a hollow boss whenever possible.

- Blend the outside corners using a radius of 25% of the nominal thickness.

- The thickness should be 50% - 75% of the nominal thickness.

- For use with self-tapping screws, the outer diameter should be 2-1/2 times the major diameter of the screw.

Holes:-

 - Limit the depth of a hole to twice its diameter.

Ribs:- - The thickness should be 50% - 75% of the nominal thickness. 

- The height should be limited to 3 times the nominal thickness.

- Ensure the top of a rib is at least 1mm (.04in) in thickness.

- Blend the base of a rib 25% of the thickness.

- Blend the top of a rib at least .25 mm (.010in)

- Space multiple ribs apart by at least twice the nominal thickness.

Snaps:- 

- Define the angle of the sloped surface on the back of the snap appropriate for either a non-locking or self-locking snap. 

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Living Hinges:- 

- Use a flexible material such as polypropylene or polyethylene.

- Consider secondary operations such as coining or flexing the hinge while the part is hot to enhance the hinge's strength.

Why Dassault Systems invent solidworks when its have best 3d CAD software like catia?

 CATIA and Solidworks both are powerful software but both have different expertise to deal with complex design that's why dassault systems have both software to stand at top in global  market. 

-> CATIA was released in 1977 and is now owned by dassault systems. It is a product lifecycle management (PLM) software which means that it manages data during product development. It improves productivity and workflow, as usually many people work on same project.

CATIA is Powerful 3D modeling software and dominating in Automotive, Aerospace and Aeronautics.

->SolidWorks is also owned by dessault systems, launched in 1995. it is basically Parametric 3D modeling software, means by changing dimension value whole design got changed. 

Solidworks have also powerful tools which increase ability to draw using either parts or assemblies, rendering and simulation and others.

Solidworks have friendly user interface and commands to use easily. SolidWorks is very popular in industrial and products design, machinery, education, railways and medical industries.

As per above given details we can conclude, CATIA is mainly using for complex design where we need to use surfacing work. Example- Automotive, aerospace etc.

on the other hand, Solidworks have ability to work with part level design, assembly and development.

So, by the both software dessault system can cover maximum market of design and development that's why it invented and getting  continuously up-gradation in both softwares to make more friendly and easy to operate with accuracy and efficiency .

Designing plastic parts for strength

 Overview:  Interior trim parts must withstand substantial pressure and stress specifically parts such as door panels and handles. This document explains various design options to help strengthen the part.

Plastic Filler Materials: Some plastics have fillers added for additional strength. These plastic types tend to be strong however, they can wear out the mold. These fillers have a tendency to wear out mold components like gates, runners, and manifold systems. They can also have effects inside the mold when having to flow around sharp corners or into small features. Some mold vendors prefer to place inserts into high wear areas making the area in question easy to replace. This tends to add more cost to the mold, but can save in the end by reducing the need to completely rebuild an entire mold.

Using Ribs for Strength: Using ribs is probably the most common way to strengthen a part. Ribs give strength to a part and prevent a part from warping. Ribs can be a challenge if they are too tall. You have to be aware of how thick a rib is at the base of the part. Ribs that get too wide at the base can produce a sink mark in the opposite side of the part. This is not good for cosmetic parts because these flaws can be apparent. One consideration is to reduce your rib versus wall thickness percentage. The general rule is to make the rib thickness 60% the thickness of the part. You can reduce this to 50% of the part thickness to help keep the thickness at the base to a smaller size.

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Coring versus Ribs:Sometimes ribs are not the appropriate tool to use. In the following example, a door handle is created and shown with its outer shape. 

In this scenario, the part needs to look and feel as if it is a solid part. The part has a thickness that is too large to mold with a multitude of flaws including sink marks and warping. If you try to shell the part and add ribs for strength, you might create a sharper edge on the backside making it uncomfortable to grasp.

In this situation, coring can be a viable solution. By removing a series of pockets on the backside, you can simulate the feel of a complete part, but have the necessary walls in it to avoid the problems.