Globalization poses major challenges for industrial production, such as greater competitive pressure or stronger demands for product customization with ever shorter delivery times. This has a particular impact on assembly. In order to increase their own competitiveness, companies often relocate the manufacture of product components or even complete assembly to countries with very low labor costs. The reserves that lie in the improvement of existing production processes are often not utilized.
Definition
According to VDI guideline 2860 (VDI 1990), assembly refers to the entirety of all processes that serve to assemble geometrically defined bodies.
It has been referred to as a separate production stage since the beginning of industrial production. Fundamental considerations can already be found in the writings of the American engineer Frederik Winslow Taylor published in 1900. With the introduction of flow assembly by Henry Ford in 1908, an extreme division of labor developed. This made it possible to counteract the shortage of skilled workers and, with a few exceptions, assembly became an unskilled labor activity.
Since then, workplaces have been made more ergonomic, labor-intensive work steps have been taken over by machines and workers have been protected during processes that are hazardous to their health. However, the assembly process has changed little as a result - compared to the enormous progress made in parts production.
Automated assembly systems developed in parallel with the development of vibratory bowl feeders, which are used to sort and feed small parts such as screws. Automated assembly requires high investments and therefore also large batch sizes. Semi-automated systems in which parts of the entire production process run automatically are also known as hybrid assembly systems.
Influence of changing market conditions
The effects of globalization and the development of the supplier market into a buyer's market are leading to a sharp increase in product variants and thus to a reduction in batch sizes. Quality requirements are constantly increasing and just-in-time delivery is becoming more and more of a necessity, while at the same time manufacturing costs must be reduced in order to cope with growing competitive pressure.
This means that assembly must become more flexible and assembly systems must be able to be adapted quickly and easily to the type and quantity of products to be produced. The proportion of reusable components should be as high as possible and variants should be created as late as possible. To this end, standardized functional assemblies and the integration of shaping production processes into the assembly process are used. In order to reduce costs, an optimum ratio between personnel costs and investments must be determined and the assembly process designed accordingly.
Manual assembly
In manual assembly (lat. manus = hand), the assembly processes are carried out by people. Consequently, optimization opportunities here lie mainly in improving working conditions and the resulting increase in employee performance.
A person's performance is influenced by many factors, including climatic and acoustic environmental conditions, the working atmosphere and, of course, the design of the workplace.
The design of working conditions in accordance with recognized ergonomic principles to prevent damage to health and make work easier is a mandatory part of the German Works Constitution Act.
Monotonous assembly processes should be supported by mechanical aids and workstations should be set up as product-neutral as possible.
Self-monitoring of the work performed by the employee also plays a decisive role. Consequently, the focus here is on people more than with any other assembly technology, and the motivation and training-related performance of employees is of great importance.
Automated assembly systems
Automated systems have been used since the 1950s, primarily for the manufacture of mass products. Today's systems are often characterized by a modular design, whereby various tried and tested assembly systems are combined in a modular system .
The possible degree of automation of a system is determined on the one hand by its technical feasibility; for example, it is easier to slide two components into each other than to glue or solder them together. On the other hand, factors such as cost, reliability and accuracy of the assembly systems used must also be taken into account.
Automatic assembly machines can basically be divided into single-station machines and multi-station machines. As a rule, they are single-purpose machines. By incorporating freely programmable robots, a certain degree of flexibility is also possible.
Hybrid assembly systems
If manual workstations are combined with automatic assembly systems, the result is a hybrid assembly system. These form the middle ground between manual and automatic assembly in terms of quantity, variety, productivity and flexibility . They are well suited to achieving high productivity in the medium quantity range and are mainly used to handle certain easy-to-automate or repetitive work steps in the production process. Due to the increasing product variance adapted to market conditions, such systems are becoming increasingly important.
The basis for hybrid assembly systems is purely manual assembly. Individual work steps are automated, for which the most economical ratio between automatic and manual methods must be determined. Care must be taken to ensure that people are not pushed into the background and that the cycle times of the automatic machines are adapted to the employees so that neither waiting times nor stress times arise.
Flexible assembly systems
Flexible assembly systems rely on the use of freely programmable joining and testing equipment. They must be able to assemble any products and variants in any order and compete with manual assembly. In contrast to manual assembly, the individual parts must be available in an orderly manner.
The peripheral equipment required for this or for the transportation of the products often significantly exceeds the basic costs for the assembly robots. A semi-automated variant in the form of a hybrid system consisting of humans and robots is usually the more economical option. The same rules apply to workplace design as for the combination of automated assembly machines with manual assembly techniques; here too, humans should not take a back seat and serve as a stopgap for the robotics.
