When is it beneficial to switch from manual application to machine application of materials?

Individual requirements are the key factor in choosing a metering and mixing system

Liquid and pasty materials offer a wide range of possibilities for permanently bonding components made from different materials, for sealing or for implementing construction requirements. When and where a metering and mixing system is used is determined by the various process parameters.

The intelligent planning of a production process does not start with the issue of manual or machine application of materials – and certainly not with ‘high-end technology’. It is far more important to understand the material properties thoroughly under different conditions as well as to define the targets with a high level of precision. Only then can the production steps be correctly described. This prevents the subsequent process from being planned out incorrectly and thus resulting in errors – regardless of whether machine processing is employed or not. Once all relevant influencing variables have been identified and targets set, it can be decided whether a person or machine should or can take care of the production process.

Manual applicators

If a new application process is installed, the first tentative steps are typically mapped out with manual applicators or cartridges. In this way, basic feasibility can be checked quickly and easily based on initial prototypes. In some industries, a cartridge, in one- or two-component forms, may always be the primary choice. For example, if bonding is to be carried out in the fuselage of an aircraft, an automatic metering and mixing system is typically not suitable from a logistical perspective, such as in the case of systems technology for 8-metre bonding. Also in the case of large-scale applications, such as in the construction and transport industries, manual solutions are generally preferable. This also applies to ‘simple’ applications that do not place high demands on the visual result or material properties.

The ‘evolution’ from manual to machine processing

The move from manual to machine processing of materials represents an important step in the ‘evolution’ of a production process. It is not possible to give a general statement as to the key criteria regarding the acquisition of a system. The primary influencing factors need to be considered in advance – but there are typically one or two factors that are decisive, which then sway things either towards or away from machine processing.

In the case of high volumes or high quality requirements that cannot be implemented manually, the investment in a metering and mixing system is worthwhile. In some cases, this can reduce running costs – for example, since less unused material is discarded and fewer rejects are produced.

An interim solution is also possible. Here, the metering and mixing solution is only used to fill material cartridges. However, this really only proves beneficial beyond a certain volume of material. The price of the material is significantly lower in this case compared to ready-bought cartridges, and there are also savings to be made in the logistics process.

Interactions between application and product

When deciding the metering method to use, the interactions between the application and the product play a key role. If the product requires high precision, this automatically means there will be high demands on the application. In many cases, the only option is machine, or possibly automated (robot-assisted), processing. In the case of manual application, there is always some uncertainty regarding whether the produced components meet the previously defined targets. Even the slightest differences in the mixing ratio can result in significant differences in the quality of the end product. For example, beads of adhesive or sealant may vary in strength or potting compounds may become susceptible to cold or humidity. In addition, beads of adhesive or sealant cannot always be applied with one hundred per cent accuracy and precision. Manual application generally involves applying more adhesive to ensure a secure bond, but risks the component not appearing nicely bonded in a visual sense. In the case of high visual requirements, manual bonding is therefore not typically an option. Furthermore, the skill level of the workers in question is an important factor. Different skills can lead to different results. There is also a risk that mistakes may be made unknowingly due to a lack of expertise. The user can quickly be the main weak point in the processing of the materials.

Consideration of material properties, handling and production steps

If components are to be bonded, for example, then an adhesive that is suitable for the joining parts needs to be identified. This relates to the consistency during the metering and joining process as well as to the subsequent hardened state. In addition, general conditions such as humidity or the temperature in the production environment play an important role. These conditions can influence the planning of the production process or the quality of the product. Timing also has a significant impact on the production process. Depending on how long adhesives or sealants and potting compounds have to harden, this is included in the planning of all upstream and downstream production steps, including the complete component handling. A polyurethane adhesive takes around seven days to fully harden. This should, of course, be factored into the calculations. When selecting the appropriate processing method, it should be considered whether a 1K or a 2K adhesive is to be used for the application.

Pre-treatment may also be necessary in advance to ensure that the surface of the component is clean and that adhesion between the adhesive and the substrate is guaranteed. In some cases, post-treatment may be necessary, for example when adhesives only harden under UV light. In addition, there are adhesives that cannot be processed manually at all because they need to be prepared. This includes degassing, temperature control and closed-loop conveying to ensure that the higher-density fillers cannot settle. Incidentally, this happens much faster at a higher ambient temperature.

Requirements for the metering process

The metering process is just one of numerous production steps involved in creating the finished product, but it is often a decisive step. The fact is that there are always inaccuracies in the metering process in the case of manual processing, while adequate monitoring is not possible.

In all areas, the demands on the quality of all products are increasing. There is increasing demand for high process reliability, consistent quality assurance and comprehensive documentation. The following factors can only be implemented with a metering and mixing system:

  • Constant mixing ratio with multiple components
  • Discharge quantity
  • Shot size
  • Defined tolerance ranges
  • Application control and documentation

In the case of high demands on the metering process, machine processing is generally the only option. It guarantees a high level of process reliability and reproducibility of the metering process at all times. The user can configure, store, monitor and document all parameters with high precision. This is particularly important if companies want to be certified and need to comply with DIN standard 2304 regarding the quality requirements of the bonding process.

Consideration of economic factors

Economic factors play an important role, of course. The acquisition of a metering and mixing system can mean a high investment depending on the size of the company. On the other hand, running costs are significantly higher in the case of manual processing. The effort involved in the production of cartridges is higher for material manufacturers, so the prices are around three to ten times higher than for 20-litre containers. In addition, processing with cartridges creates a lot of material waste and unnecessary rubbish. Often, the cartridges cannot be properly emptied and need to be disposed of in the form of hazardous waste. Larger containers and less waste can therefore save material and thus costs. Resources are used efficiently and there is less impact on the environment. Often, the application of materials with cartridges also takes considerably longer than with a metering and mixing system, as the cartridge first needs to be filled or replaced. Another important factor is the product value itself. If the products or components have a very high value after bonding, then the losses will quickly add up if there are rejects due to quality defects. The higher the additional value created through the bonding or potting process, the more care is needed for the metering process. This means that investing in a metering and mixing system may also be beneficial in the case of smaller quantities.


Ultimately, the production process is determined by the material properties and the targets for the end product. The technical options or the costs and benefits therefore always need to be reassessed in each individual case. Depending on the application, the error rate in the case of manual processing with cartridges may be higher than with machine processing using a metering and mixing system. The latter is more expensive to purchase, but it can pay off for numerous reasons. If the company has to comply with certain level of process reliability, quality assurance and documentation requirements, then a metering and mixing system is really the only option. In the case of low volumes or where the visual aspect is less important, manual application can be a lot more efficient. All in all, individual aspects or several factors taken together can sway the decision for or against the use of a metering and mixing system. In the next article, we describe the specific steps in the move to machine processing of materials and explain what you need to consider when purchasing a metering and mixing system.

Your partnership with DOPAG

  • One contact for the entire system solution
  • All applications from one provider
  • Implementation of specific requirements and automation
  • Competent support from DOPAG experts
  • A dedicated technical centre for testing and customer training
  • Close collaboration with material manufacturers
  • Decades of experience in metering and mixing technology
  • Global distribution and service in over 40 countries

Reference projects


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