Being an industrial designer, it's impossible to deal with crafts and materials. Commonly used materials and related crafts need to be studied, understood and mastered. If you want to be promoted to designer, those are only paths to success. . The following is a summary of process knowledge and analysis of 19 plastic bonding methods. Plastic, a traditional material, is widely used in medical equipment, automobiles, mobile phones and other consumer electronics and daily products. The end use characteristics of plastic parts depend largely on how plastic parts are joined. After a long period of research and practice, scientists and allied engineers and technicians have developed many different methods for joining plastics.

This article provides a brief introduction to these plastic jointing technologies. It is hoped that it can serve as a guide for designers in related fields when choosing plastic bonding methods.

1. Adhesive connection

Adhesive bonding refers to technology of joining surfaces of homogeneous or dissimilar objects using adhesives. Adhesive bonding refers to adhesion and cohesion of interface, which can be two or more Class A natural or synthetic, organic or inorganic substances, which are connected to each other by parts or materials, which are collectively referred to as adhesives, also known as adhesives, which are commonly referred to as glue. In short, an adhesive is a substance that can bind adhesive joints through bonding.

2. Solvent connection

This means that solvent dissolves plastic surface to mix materials between plastic surfaces. When the solvent evaporates, a compound is formed.

3. Fixing connection

Fastening refers to use of fasteners to connect plastic parts, including press-in fasteners, self-tapping screws, and bolted connections. Plastic parts, commonly referred to as press-in parts, are connected by some kind of protrusion on stem, which forms an interference fit in plastic cavity. Self-tapping screws use self-tapping threaded connections without threaded holes.

4. Swivel

Plastic hinges can be divided into three types: one-piece integrated hinge, two-piece integrated hinge and a composite combined hinge. Among them, a one-piece integrated hinge is realized by molding two parts as a whole without other additional parts. The integrated two-piece hinge firstly processes two separate plastic parts by injection molding and then connects them by assembly. In addition to machining two separate plastic parts, compound hinges also need to use additional parts such as hinge components such as rods or metal.

It has advantage that it can be opened and closed repeatedly, and built-in hinge is usually designed in a box or close to inside, which reduces overall size of part; disadvantage is that forming mold requires high precision. and form is generally more complicated and requires a lot of resources. To gain experience in rational design of living loops.

5. Insert molding

Insert molding refers to a casting method in which pre-prepared inserts of various materials are placed in an injection mold, resin is injected, and molten material and inserts combine and solidify to form an integrated product. Among them, thread inserts are main way to obtain threads in plastic parts, which can provide better connection strength than self-tapping threads. Inserts are not limited to metals, but also include fabric, paper, wire, plastic, glass, wood, coils, and electrical parts. Insert molding uses a combination of resin insulation and metal conductivity, and molded products can perform main functions of electrical products.

The technology of decorating inserts by injection molding - IMD (In-Mold Decoration). Currently, IMD is a popular surface decoration technology in world. Mainly used for decorative and functional control panels of household appliances, car dashboards, air conditioning panels, mobile phone cases/lenses, washing machines, refrigerators, etc. are widely used. IMD is a technology that places printed and formed decorative sheet into an injection mold, and then injects resin on reverse side of formed sheet, so that resin and sheet are combined into one curing molding technology.

OcThe new advantage of injection molding is that combination of ease of molding and flexibility of resin with rigidity, strength and heat resistance of metal can be made into complex and exquisite integrated metal and plastic products.

6. Multi-component molding

Multi-component injection molding is also called two-color injection molding, which refers to method of molding two different colors of plastic into same mold. It can make plastic parts have two different colors, and can also make plastic parts regular patterns or irregular moiré patterns to improve practicality and aesthetics of plastic parts.

The figure below shows principle of two-color injection molding. It has two cylinders, each of which has same design and purpose as conventional injection molding cylinders. Each barrel with material has its own channel for communication with nozzle; an opening and closing valve is also installed in nozzle channel. During molding, after plasticizing molten material in cylinder, sequence of molten material entering nozzle and ratio of material exiting are controlled by opening and closing valve, and then injected into mold cavity from nozzle. Various plastic products with different color mixing effects can be produced.

7. Cast screw connection

Molded thread connection refers to direct molding of a thread on a plastic part by mold design, and then realizes connection with other threads with same tooth shape, nominal diameter and other parameters.

The threads on plastic products are divided into two types: external threads and internal threads. External threads are usually machined with sliders, while internal threads are extruded by twisting teeth. Among them, external thread structure is relatively simple. After product is formed, there will be parting line marks on plastic product. If parting line marks are obvious, it will affect product appearance and thread fit. . The principle is to slide under action of inclined guide column, and then ejector pin ejects product. Molds with internal thread can be divided into:

1. Forced breakout structure (non-rotating).

2. Non-forced twisting (rotary type). The current spun thread is mainly used in production of bottle caps.

8. Threaded connection

Plastic tapping is drilling a hole in a plastic part, then cutting a thread to form a thread, and then using thread to connect to other parts, which is similar to connecting to metal.

Its advantages: process does not impose any requirements on shape of plastic parts, and exact positioning of holes can be obtained using precision mechanical tools.

9. Close Fit

A pressure landing is also called a force landing, an interference fit, and an interference fit. The shaft and hole, whose assembly relations are related to interference fit, are assembled together under a certain pressure. It is also possible to heat hole to widen hole, or shaft is cooled to reduce size of shaft to assemble between two parts, and an interference fit occurs when two parts return to same temperature after assembly. It uses elastic deformation of hole and shaft of connected plastic parts, and can transmit a certain torque or axial force after assembly.

10. Quick connection

A buckle is a mechanism used to integrally connect or integrally lock one piece and another piece. It is commonly used to connect plastic parts, and its material is usually made of plastic with a certain flexibility. The biggest feature of snap connection is that it is easy to install and disassemble, and it can also be disassembled without tools.

Generally speaking, buckles consist of fixing parts and clasps. The function of positioning part is to guide buckle to reach installation position smoothly, correctly and quickly during installation. The function of clasp is to fix buckle to backing and ensure that it does not fall off during use.

According to different use cases and requirements, fasteners are divided into removable and non-removable. Removable fasteners are usually designed so that when a certain separating force is applied, latch is released and two connected parts are separated. This type of buckle is often used to connect two pieces that need to be taken apart frequently. Fixed fasteners require artificial deflection to disassemble two parts, and are mainly used to connect and fix parts without disassembly during use.

11. Welding of plastic rivets

Riveting is especially used to connect parts made of dissimilar materials (such as plastic and metal). One part has studs that fit into holes in other part. The stud is then deformed by cold flow or melting of plastic, forming a rivet head that mechanically holds two parts together. By changing design of welding head, it is possible to obtain various designs of rivet heads.

Cold riveting: pCold riveting uses high pressure to deform stud. Cold flow creates high stresses in stud area and is therefore only suitable for more ductile plastics.

Hot riveting: Hot riveting heats up head of compression weld, so less pressure is required to form rivet head on stud and less residual stress is generated in rivet head. Can be applied to a much wider range of thermoplastic materials than cold riveting, including glass-filled materials. The quality of its connections depends on control of process parameters: temperature, pressure and time.

Hot air riveting: In hot air riveting, stud is heated by a stream of superheated air, which transfers heat through air ducts around stud. The independent cold welding head then lowers, compressing stud.

Ultrasonic riveting: In ultrasonic riveting, a stud is melted using ultrasonic energy delivered by a horn. During continued pressure of horn, molten material of stud flows into cavity within horn, forming desired shape of rivet head.

The process of welding plastic parts

The principle of welding is same. First, heat joint surface of two plastic parts to be welded until it melts, then increase joint pressure on surface to be welded and maintain a stable pressure for a certain period of time. until welding surface hardens, i.e. welding is successful.

12. Induction welding

The main use of high-frequency equipment, high-voltage rectification, self-excited high-frequency oscillation of tube to instantly create an electric field of electromagnetic current, and use of processed PVC, TPU, EVA, PET and other plastics and plastic materials to create a pole in internal molecules of plastic and plastic materials in electromagnetic wave electric field. Individual frictional heat plus a certain pressure to make plastic and plastic products that need to be heat-sealed and welded, to achieve welding effect.

13. Rotation welding

The Rotary Plastic Friction Welding Machine is generally used to weld two round thermoplastic workpieces. During welding, one workpiece is fixed on lower mold half, and other workpiece rotates on surface of fixed workpiece. Due to a certain pressure acting on two workpieces, heat generated by friction between workpieces can melt contact surfaces of two workpieces and form a strong and tight joint. Among them, position-rotation melting is to rotate at set time, stop at set position momentarily, and change to constant melting.

14. Hot plate welding

Hot plate welding consists in fact that sides of two plastic parts to be joinedLei is placed on a heating plate with a thermostat to heat until surface is melted, and then two softened surfaces are pressed together with slight pressure to form plastic parts. In addition, there is a widely used hot plate heat sealing process. First, two parts to be joined are stacked together, and heat sealing plate is heated with electric heating tubes, etc., and heat sealing plate is lowered onto top of two parts .Applying a certain pressure, heat seal will melt contact area of ​​the two parts and then harden to join them together. This process is mainly used for sealing joint of polymer resin film and plastic parts.

15. Hot gas welding

There are three methods of hot gas welding: spot welding, continuous hot gas welding and extrusion welding. Their basic principles are same. The wind generated by motor takes heat generated by heating wire to obtain a hot air stream, so that two plastic parts to be welded and welding rod are heated and bonded together into a molten state, thus achieving purpose of welding. Where spot welding is used to join parts before permanent welding.

Spot welding is a temporary welding of materials that can be done without electrodes and requires use of spot welding tips.

For continuous welding, an electrode of same material as part being welded is used, and tip is rapidly fanned back and forth across weld zone until V-groove and electrode are soft enough to weld, usually pressed against each other to friend. with heated roller. Extrusion welding means that filled resin is either fed from a hopper as pellets or fed as welding rods to a barrel and then extruded from a single screw melting chamber driven by an electric motor heated by electric heating. coils or hot gases. The joint surface is heated by a hot gas heater connected to extruder, and finally filling resin is melted and bonded to parts to be welded.

16. Ultrasonic welding

Ultrasonic welding is conversion of current with a frequency of 50/60 Hz into electrical energy with a frequency of 15, 20, 30 or 40 kHz using an ultrasonic generator. The converted high-frequency electrical energy is converted into mechanical motion of same frequency through converter, and then mechanical motion is transmitted to welding head through a set of horn devices capable of changing amplitude. The welding head transfers received vibration energy to joint of part to be welded. In this area, vibration energy is converted into thermal energy due to friction, causing contact surface of two plastics to quickly melt, and afterNogo pressure is applied, it will merge into one. When ultrasonic wave stops working, let pressure continue for a few seconds to solidify and form, thus forming a strong molecular chain to achieve purpose of welding, and welding strength can be close to that of raw materials. Ultrasonics can be used not only for welding hard thermoplastics, but also for processing fabrics and films.

The main components of an ultrasonic welding system include an ultrasonic generator, a triple transducer/horn/welding head, a mold and a frame.

The quality of ultrasonic welding of plastic depends on three factors: amplitude of transducer welding head, applied pressure, and welding time. The welding time and pressure of welding head can be adjusted, and amplitude is controlled by transducer and horn.

17. Vibration welding

There are six process parameters in vibration welding process: welding time, holding time, welding pressure, amplitude, frequency and voltage.

Vibration welding is divided into linear vibration welding, orbital vibration welding and angle vibration welding.

Linear vibration friction welding uses thermal energy of friction generated at contact surface of two parts to be welded to melt plastic. Thermal energy arises from reciprocating movement of workpiece on another surface with a certain displacement or amplitude under a certain pressure. Once desired degree of welding has been achieved, vibration will stop, and at same time, a certain pressure will still be applied to two workpieces to cool and solidify newly welded parts, thereby forming a strong joint.

Orbital vibration friction welding is a welding method that uses thermal energy of friction. In orbital friction friction welding, top part rotates at a constant speed—circular motion in all directions. The movement generates heat, which brings welded part of two plastic parts to melting point. As soon as plastic begins to melt, movement stops and welded parts of two parts harden and are firmly connected to each other. Low clamping forces result in minimal workpiece distortion, and workpieces up to 10" in diameter can be welded using orbital vibratory friction.

Field vibration welding means that workpiece rotates around a fulcrum. There are currently several mass-produced machines for corner vibration welding.

18. Laser welding

Laser welding is a technology in which thermoplastic sheets, films or molded parts are joined together by melting contact surfaces of plastics using heat generated by a laser beam.

It first appeared in 1970s, but due to its high cost, it cannot compete with earlier plastic bonding technologies such as vibration welding technology and hot plate welding technology. However, since mid-1990s, due to decreasing cost of equipment required for laser welding technology, this technology has gradually become widely welcomed by people.

When plastic parts to be bonded are very fragile materials (such as electronic components) or require a sterile environment (such as medical devices and food packaging), laser welding technology can come in handy. Laser welding technology is fast and especially suitable for processing automotive plastic parts on a conveyor. In addition, for joints of complex geometries that are difficult to join with other welding methods, laser welding technology can be considered.

The main advantages of laser welding: welding equipment does not need to contact plastic parts to be glued, high speed, high degree of equipment automation, very convenient for processing complex plastic parts. ; there will be no flash; welding is strong; high-precision welded joints can be obtained; vibration-free technology; air-tight or vacuum-tight construction can be produced; minimize thermal damage and thermal deformation; you can use resins of different composition or color. tied together.

19. Hot wire welding

Hot wire welding, also known as resistance welding, uses a wire to transfer heat between two plastic parts to be joined in order to melt surfaces of plastic parts and apply a certain amount of pressure to join them together.

A metal wire is placed on one of surfaces of parts to be joined. When current passes through metal wire, its resistance is used to heat metal wire and transfer heat to plastic part. The wire remains in plastic product after welding, and part protruding beyond joint is cut off after welding. Typically, grooves or other positioning features are provided on part to ensure correct position of wire.