The acquisition time of parts depends largely on the design nature and assembly method of assembly area. For small parts placed where assembly workers can easily reach them, if desktop assembly or multi-station assembly is used, the assembly time is sufficient. In both cases, it is assumed that the assembler does not need to move the body.
For large-volume parts that are not suitable for the transmission system, and if the assembled parts weigh more than 5 pounds or the volume exceeds 12 inch, it is impossible to place enough parts where workers can easily reach them. In this case, assuming that the maximum part size does not exceed 35 inches and no part exceeds 30 pounds, a micro-assembly center can be used. There is a workbench and a storage rack in the center, with parts on it, which is as convenient as possible for people to operate. However, it may increase the operation time because of the need to turn around, bend over or walk around in the process of obtaining some parts. It is very convenient to set up three micro-assembly work centers for three types of assembly, and the maximum assembly size is no more than 15 inch, 15-25 inch and 25-35 inch respectively.
Traditional assembly design can be used for products with larger parts. In this way, the products are assembled on the workbench or floor, and all kinds of shelves and auxiliary equipment are reasonably arranged around the assembly area. The whole working area is larger than the assembly center of micro parts, and its size depends on the size and model of the largest part in the assembly. Three traditional assembly design types can be used to assemble parts with specifications of 35-50 inches, 50-65 inches and over 65 inches.
At the same time, for large products, we can adopt more flexible layout, which is called flexible assembly layout. The layout is similar to the traditional assembly layout in specification, and three different models can be selected according to the size of the largest part. However, the use of mobile storage trucks and work trucks can improve assembly efficiency.
In traditional assembly and flexible assembly design, mechanical assistance, such as cranes and trolleys, may be needed. In this case, it may be necessary to expand the work area to provide additional equipment. For large-scale assembly of products including large parts (such as in automobile industry), production lines that move between manual assembly stations can be adopted.
There are also two cases of manual assembly: one is the assembly of small batches and small products that may be carried out in the cleaning workshop, including the assembly of complex and sensitive equipment, such as the assembly of aircraft fuel control valves. Every step depends on the operating instructions, and the workers are close to the starting point of the learning curve. Secondly, the assembly of large-scale products is carried out on site. This type of assembly is usually called "installation". For example, assembling and installing elevators for high-rise buildings is an example.
In any assembly situation, special equipment may be required. For example, it is sometimes necessary to use positioning equipment to position and adjust parts, especially before welding operations. In these cases, the equipment must be transported to the assembly area and transported back after the parts are positioned and fixed. In this way, the running time of the equipment is almost twice that of the parts. If the batch of products produced is not large, the running time of the equipment must be considered.
Summarizing the basic types of the above manual assembly methods, we can see that the first three methods are only used for the assembly of small parts. In these cases, it can be assumed that all parts are within reach and can be obtained one at a time. Therefore, it is not good to insert six screws and get six screws at the same time. However, for the assembly of products with large parts, small parts such as fasteners may be placed in inaccessible places, or assemblers must move to different positions to obtain them, so it may be quite beneficial to obtain multiple parts when necessary.
automatic assembly
Assembly in the production process includes assembling all parts and components of a specific product, fixing the product, performing performance tests and functional tests, labeling, distinguishing good and bad packaging and preparing for final use. Compared with machining methods such as cutting, grinding and welding, assembly is unique in that most of these processes only include a few or even only one rule. Without equipment, most of these non-assembly operations cannot be carried out. Therefore, the development of automatic assembly method is inevitable, not dispensable. On the other hand, it may be necessary to use a variety of fixing methods to assemble on the machine, such as riveting, welding, threaded connection and using adhesive, as well as automatic selection, detection, measurement, function test, marking and packaging. The present situation of assembly operation technology has not reached the standard level, and a large number of manual operations are still used in this field.
Matters needing attention in automatic assembly:
Before adopting automatic assembly, several factors need to be considered. It includes the practicality, economic factors and rationality of process automation, simulation, management and labor relations.
When deciding the practicability of automatic assembly, the following factors need to be carefully considered:
Number of parts in the assembly
Part design (material, shape, specification, volume tolerance and weight) related to productivity, assembly capacity, automatic handling capacity and inspection capacity.
Quality of assembly. Out-of-tolerance or defective parts will cause production losses and increase costs due to failure.
Qualified and skilled personnel are required to be responsible for the operation of the equipment.
Total output and productivity requirements.
Product type and frequency of design changes.
. The required joining method.
. Assembly time and cost.
. The layout of the assembly line or system should be simulated, including material handling.
For successful and economical assembly, products that are usually simple, small and have a fairly stable design life are the best choice. This product is usually large in size, with high labor content and/or high rejection rate due to manual assembly. The development of flexible program-controlled robot assembly system can reduce the requirements for production and product life and automatically assemble product design.
In order to assemble successfully, effectively, economically and automatically, it is very important to optimize the design or redesign of products and components. Usually, a considerable amount of money is spent on the automation of existing product design and assembly, and it is more economical to redesign products to promote automatic assembly. Assembly design has been applied continuously, because it realizes potential production savings and high quality and reliability of products.
When evaluating product design to improve assembly, close cooperation between design and production engineers is needed. In addition, in the early design and redesign stage, it is necessary to consider the inherent capabilities and limitations of assembly operations. It is also recommended to evaluate the components that provide positioning at the earliest possible design stage. Various designs and assemblies should be evaluated and simplified.
The best product design is one that can minimize the assembly requirements or the number of assembly parts. A single stamping part replaces the design of two-piece components, which usually reduces the total cost of products and components.
When one-component products do not exist or are uneconomical, the number of required parts should be as small as possible and the complexity should be reduced. However, two or more components are rarely produced instead of one component, which is more economical. The reason for reducing the number of parts is to make the remaining parts play a greater role and reduce the number of idle parts. To determine whether a part has been removed, you should answer the following three questions:
1. Does this part move according to other parts?
2. Is this part made of different materials compared with other parts?
3. Do parts need to be moved for product maintenance?
A positive answer to any of the above questions usually means a negative answer, which means that this part may be redundant and its role may be transferred to a more important part. Convenient automatic assembly design.
Parts designed for automatic assembly should be easy to handle, fill, orient, locate and combine. Parts that are easy to orient should include:
1. Completely symmetrical parts, such as spheres, cylinders, disks and rods. Generally speaking, the length of a cylindrical part should be 25% longer or shorter than its diameter to facilitate filling.
2. Parts with obviously disproportionate weight or volume, such as flat head screws, bolts and rivets. The center of gravity should be close to one end of each part, thus creating a natural filling trend in a specific direction. If the natural orientation is not the ideal position, it should be quite easy to rotate the part to the appropriate position.
Assembly machinery and assembly system
Automatic assembly can use a variety of machinery and systems, which is the general outline of some concepts. In addition, this paper will also discuss the combination of these basic systems, as well as flexible assembly system and robot assembly system.
Single station assembly
When a specific operation is performed on one or several parts for many times, the mechanical equipment using a single workbench is more extensive. A common application is to assemble many parts into a unit, such as inserting blades or blades into a turbine or compressor wheel. When performing different operations, these machines can also be used if the required tools are not too complicated. These machines are also used in multi-station assembly systems.
Synchronous assembly system
Synchronous (transposition) assembly system appears in the form of disk (rotation), in-line assembly and disk deformation. With these systems, all platens or parts move the same distance at the same time. Since the bit interval is determined by the slowest operation on any workbench, the operation time becomes a decisive factor affecting productivity. The operator can't change the productivity, and the interruption of any station will cause the whole assembly line to stop production. Proper consideration of balanced assembly line and parallel assembly operation will reduce failure problems.
Asynchronous assembly system
Asynchronous transfer (cumulative or unpowered) assembly system, with free and moving trays, workpieces and independent workbench, is widely used in places where the time required for different operations is very different and large products with multiple parts are processed. Compared with the * * * machine, the cycle of the machine is slower, but the slower station can be equipped with double cutters or three cutters to improve productivity. One of the main advantages of these so-called dynamic freestyle systems is that they enhance versatility. Independent work stations that operate independently only work when trays are provided as required and manual and automatic operations are easy to combine. Different ways can be used to meet the needs of line balance. For example, a multi-stage loading, assembling or testing platform can be arranged or transported to a multi-stage track for longer operation, while a short operation can be completed in one operation. Non-* * machines usually have lower original cost, but they need more control equipment (one for each station) and generally need more space.
Continuous motion system
Under the condition that the workpiece or pallet runs at a constant speed and the working head reciprocates, the assembly operation is performed by using a continuous motion system. Because the transposition time is eliminated, high productivity can be obtained. However, because the working head must run synchronously with the assembled products, this increases the cost and complexity of the system. The continuous motion system has limited application except for mass production in packaging and bottling enterprises. However, the system is still used to manually assemble large and heavy products, such as cars and refrigerators, and the operators move with the products at work.
Turntable (rotary) assembly system
The synchronous design of turntable or rotary transposition machine is an early assembly scheme, which is still used in many occasions. Worktable and cutter can be placed on the center table or around the transposition table. Generally speaking, the system is only used for small, medium and light components, which require relatively few and uncomplicated operations. With the increase of the diameter of the transposition table, its quality and complexity become unrealistic. Another disadvantage is that it is difficult to operate the indexing table, indexing mechanism and console with the central bed design, and it is inconvenient to use the table and tools.
On-line assembly system
Online assembly system can be used for synchronous (transposition), asynchronous (cumulative or dynamic freestyle) and continuous design. In-line assembly machinery has winding or lifting type, as well as traditional automatic production line. In the lifting type, the tray or working head bearing the parts moves horizontally along a straight line; When it is empty, it is sent back to the loading platform by the conveyor belt under the machine. In the circular type, the machine moves around the edge of the machine along an elliptical, rectangular or square route.
Optical disc assembling machine
Flexible assembly system
The market demand and the shortening of product cycle lead to increasing product differences, which requires the automatic assembly system to be more flexible. The demand for large long-life products is decreasing.
A lot of work has been done to develop a more flexible assembly system that can handle smaller batches and diversified products, and it is still going on. The objectives of the system include improving cost-effectiveness and reducing depreciation of basic equipment.
A developing concept is the use of automatic guided vehicles (AGV), which are currently used for small-scale and large-scale assembly. Equipment such as automobiles and household appliances are usually driven independently by electricity or compressed air. They are electrically driven by cables laid under the floor, and any required route to each assembly station is controlled by computer. The cost of AGV and its control system limits their application in large-scale assembly of small parts. Combining the automatic guided vehicle with the designed workbench can bring greater flexibility.
The two main types of flexible assembly systems are programmable systems and adaptive systems. These two types include those systems that use industrial robots.
Robot assembly system
Industrial robot is a program-controlled manipulator, which can accomplish a variety of tasks. An efficient robot assembly system needs to carefully consider the transmission of parts to the workstation, the feeding and positioning of parts, and the robot terminal control device. Sensing requirements and system control issues.