Steinbeis experts use automation technology to pick and pack modeling clay
Lots of kids get excited about Play-Doh and other modeling compounds. It’s a great way to allow young ones to play and explore their creativity, develop spatial thinking, and hone their motor skills. Producing modeling clay is a complex process involving multiple stages. Experts at the Steinbeis Research Center for Automation, Lightweight and Process Engineering (ALP) have been helping fine-tune the process of picking and packing modeling clay using a fully automated picking device.
A smart ejector module
The process of producing modeling clay starts with a lump of material comprising waxes, fillers, and pigments, which are first mixed in a kneader, extruded to form a bar of clay in the required diameter, and then cut to length. “As processes, mixing and extrusion are both highly efficient, so with just one of each machine it’s possible to cover a significant share of market demand,” reveals Steinbeis Entrepreneur Professor Dr.-Ing. Wolfgang Nendel.
To offer ranges of up to ten different colors, it is therefore important to be able to put products into intermediate storage before picking and packing. To do this, bars of clay in storage are placed into packaging containing different numbers of bars in the color combinations requested by customers. With parameters such as bar diameter, length, number, color combination, single-layer or double-layer packs, order picking requires a high degree of flexibility due to the large number of product variants, as well as different batch sizes. “With the current difficulty recruiting workers, especially in areas with weak business infrastructure, but also rising labor costs – and at the same time, less time to implement sometimes complex processes – automation is an absolute necessity, even for medium-sized companies,” explains Steinbeis Entrepreneur Mirko Spieler.
To make this a reality in the production of modeling clay, to minimize time investment and effort, and to improve manufacturing depth, the Steinbeis Research Center for Automation, Lightweight and Process Engineering (ALP) joined forces with the chair of lightweight structures and plastics processing (SLK) at Chemnitz University of Technology to develop and set up a fully automated picking and packing system.
Flexibility based on modularity
The new system has been kept adaptable by basing it on modular principles. This allows a whole host of product ranges to be picked. The first module folds cardboard into five carrier units, which are then packed by ten identical modules, each inserting one or two bars of modeling clay. The system allows each module to be programmed to insert a specific number of bars, in a specific position, with a specific number of layers. There is no need to program the color sequence, which is determined by the placement of the modules, and contents are moved between different stations on a conveyor belt. To ensure the modeling clay is handled safely during the subsequent packaging process, pack contents are compressed so that the bars adhere to one another and no longer lie loose in the carrier units.
Efficient generation of the process vacuum
The energy consumption of the production unit is an important factor for the economic viability and environmental friendliness of the manufacturing process. Due to the flexibility of the modules in the order picking system, the process of creating a vacuum to handle the modeling clay needs to take place in a different area. This has been made possible by generating compressed air pneumatically away from the unit, although conventional vacuum ejectors do consume large amounts of compressed air and energy. Using efficient and smart ejectors, which work without having to extend pneumatic components, makes it possible to cut consumption by up to 90% – one of the main reasons why the Steinbeis experts from Chemnitz and their project partners also adopted this solution. In addition, efficiency was improved by using three-stage vacuum ejectors, which require less compressed air and generate much higher vacuum flows, as well as valve technology to regulate pressure and only allow compressed air to be switched on and create a vacuum when vacuum levels fall below a set value.
Converting a conventional process into an automated process
One particular challenge for any medium-sized enterprise lies in expanding existing production processes to incorporate automation technology at the end of the production chain. When processes are automated, it takes a great deal of effort to deal with errors, tolerances, and inaccuracies going back to previous work steps, which until that point were corrected as part of manual processes or deemed insignificant. In most cases, requirements relating to automated processes, for example regarding precise storage, are more challenging than product quality requirements.
In addition to the high number of variants in terms of length and diameter, compared to workpieces made of plastic or metal, bars of modeling clay also involve significantly wider ranges of dimensional tolerance. Both of these factors must be taken into account and compensated for in the picking and packing process. Not only is it necessary to ensure processes are reliable – and as far as possible uninterrupted – but they must also comply with quality standards.
To meet this challenge, the project team focused on a sensor concept revolving around process monitoring and process control. They also ensured staff shared responsibility for quality issues. There were two potential options. The first was to use variable and adjustable sensors. The second was to use measurement criteria that could largely be recorded independent of the specific variant or the tolerances of bars of modeling clay. The latter option significantly reduces effort involved, as well as sources of error during changeovers.
This is something that is particularly evident when pincer technology is used to pick up and put down materials: To control processes properly, it is important to ascertain both the position of pincers and their current status. Pincers use a vacuum to seize objects and this can be detected via pressure switches, irrespective of the dimensions of a bar of modeling clay. The much greater challenge is to detect and evaluate movements, because the diameter tolerances of modeling clay can lead to deviations in gripping positions as little as several tenths of a millimeter; deviations caused by the type of bar of modeling clay lie in the range of a few millimeters; deviations caused by picking up and putting down modeling clay can be several centimeters. If sensor signals need to be generally applicable to all types of modeling clay or packaging sizes, without adjustment, it is only possible to detect movements of the pneumatic actuator, and not tolerance compensations.
Employees are responsible for correct color assortment and the position of the bars of modeling clay on the carrier units, since the position of bars on the conveyor cannot be guaranteed by the assembly, storage, and transport process. This area of overlap – between the automatic and the conventional process – was a key challenge when it came to the success of the project, in both technical and economic terms, as well as integration of the automated system into the overall process of modeling clay production.
Special materials, special processes
Automating processes involving special materials poses particular challenges for small and medium-sized companies. Machines are often unable to address requirements of a mechanical, thermal, or chemical nature, making it necessary to conduct extensive and cost-intensive development to solve the problems caused by specific materials. For example, modeling clay has a particular tendency to adhere to almost all materials it comes into contact with, except silicone and PTFE. This is especially the case at certain temperatures, and this property makes it much more difficult to remove modeling clay, as pincer movements cause damage to the modeling compound. It also displaces and places heavy loads on carrier units and it cannot be guaranteed that materials will not become detached. However, coating carrier units or making a small sideways movement with the pincer before lifting results in flaking occurring between the modeling compound and the carriage unit, resulting in separation.
Given the high number of required carrier units, coating costs have a crucial influence on the cost-effectiveness of the overall process. It is therefore not possible to use expensive PTFE or silicone coatings.
Another issue is that any coating materials transferring to the end product must not impair the quality of the play dough. To strike a healthy balance between affordability and the required technical properties, a coating was used containing a kind of wax that is very similar to the wax mixed into modeling clay. This wax can be sprayed on in a molten format or applied cold.
Made-to-measure automation solutions for SMEs
To be used by SMEs, automation technology needs to be adapted. Standard solutions meet neither the technical requirements of the kind of special materials typically processed by SMEs, nor economic requirements, especially when it comes to investment costs and anticipated flexibility and operability. This is possible, however, for one-off machines equipped with individual solutions, which not only help improve productivity but also address the shortage of skilled workers.
Contact
Prof. Dr.-Ing. Wolfgang Nendel (author)
Steinbeis Entrepreneur
Steinbeis Research Center Automation, Lightweight and Process Engineering (ALP) (Chemnitz)
Mirko Spieler (author)
Steinbeis Entrepreneur
Steinbeis Research Center Automation, Lightweight and Process Engineering (ALP) (Chemnitz)
Christoph Doerffel (author)
Assistant
Steinbeis Research Center Automation, Lightweight and Process Engineering (ALP) (Chemnitz)
223074-27