Lego-like technologies in manufacturing power distribution boxes for contemporary radar station

Introduction

From the early days of the radio-electronic industry until the present, the production of component parts of high-power radio electronic systems (RES) remains a high-cost process primarily due to the nature of the product. Typical devices within a system contain hundreds or even thousands of individual parts and assembly units, and net production of such devices can comprise only several tens of pieces per year. In this case we can refer to small-scale and, moreover, singlepart production.

The type of production is defined by the coefficient of operation assignment to one workstation or unit of equipment (series production coefficient) [1]:

where O – the number of various operations;
Р – the number of workstations where operations are executed.

The existing types of production are characterized by the values of Kз.о coefficients presented in Table 1.

Table 1

Dependence of operation assignment coefficient on production type

The lower the value of K_з.о is, the narrower the specialization of the employee is, the higher the possible degree of production automation and, as a consequence, labour productivity is. Today, low-skilled workers are employed to perform a single elementary operation at each workstation of mass production. At that, special high-performance equipment is used, which is arranged along the fabrication process (FP) and connected into a single flow line by conveyors.

As series production decreases, the principles of operation concentration are applied when groups of operations are performed at one workstation and universal multi-purpose equipment is more widely used. It is cost-effective for a multiproduct medium-scale production to use flexible manufacturing systems, where computer-aided manufacturing systems (CAM) and automated process control systems (APCS) are used.

In the production of devices within RES, the value of K_з.о often reaches hundreds of operations per workstation, and the number of manufactured articles and sizes of operational component part batches arriving at workstations are counted in units and tens of pieces. The established methods of achieving high labour productivity are virtually inapplicable to this type of production, since the manufacturing limits of differentiation in batch production are determined by the need to obtain a finished assembly unit as a result of a series of operations performed at the workstation, rather than by the required rhythm.

Process operations of irregular frequency are performed at workstations where universal equipment is used and 60 % or more of the time is spent on mechanical assembly and wiring operations. This requires highly qualified personnel, ensuring the quality of the products, which is ultimately the reason for the high cost of equipment. Table 2 shows labour input and cost of assembling a distribution cell (800 elementary operations), performed by personnel of varying qualification: wiring electricians of the 2nd–5th categories.

Table 2

Labour intensity and cost of distribution cell assembly performed by employees of different skill levels

In the present article an approach to establishing a process for single-part and small-scale production is suggested. Application of the approach can significantly reduce the time of articles production, including, but not limited to, involvement of medium-skilled personnel. For this purpose, let us consider the life cycle of systems and pay attention to the stages of development, then recall toy construction sets and their assembly instructions, and finally, establish the concept of process development technology for small-batch production on the basis of the method used for developing such assembly instructions. The first results of applying the new technology looked stunning: the average labour input of a medium-skilled assembler to assemble a cell using standard instruction cards for a batch of 10 pieces was approximately 36 man-hours, but with the use of the new type of production flowcharts, the cell assembly was performed within one two-shift working day. Results and review of the nearest prospects of the proposed technology are covered in the section “Developing 3D Fabrication Documentation and Assembly Productivity”.

Stages of system life cycle

The emergence of a ground-breaking discipline of applied systems engineering, the subject of which is the methodology of development and implementation of such systems, became a universal response to the growing needs of modern economics in technically complex equipment and systems. The concept of systems engineering providing a unified approach to the design, creation and functioning of a system is used in Russia. This approach is based on reductionism, decomposition of complex problems into simpler ones, of products – into component parts, and of projects (systems) as a whole – into phases of implementation or a life cycle [2].

The decomposition block-chart given in Fig. 1 can be applied to define the reserves for reducing the cost of a material product (devices within RES) and as a process frame structure when creating a new intellectual product.

Fig. 1. Stages of a high-tech product life cycle

With constant research expenses, the cost of the devices will be mainly determined by production costs (at the creation phase) and the production preparation costs at the stage of design and, partially, at the stage of development.

A decisive role in achieving production goals is played by the development and effective description of the process, i.e., the sequence and contents of activities (process operations) to obtain finished product. The level of process description detail depends on the production type. Mass production requires an exhaustive description of all process operations in the sequence of their execution with indication of transitions and process modes given in the instruction cards. At the same time, high cost of process preparation of production is compensated by reduction of direct manufacturing costs. With the decrease in series production and increase in concentration of production, the share of preparation costs goes up and it is necessary to take actions to reduce them at the expense of process development funds, among other methods.

The outline display of the sequence of actions with the minimum level of detail becomes cost-effective. For small-scale production, workflow or workflow and operational process descriptions are used, while workflow charts are applied as the basic fabrication documents. In the first case, a workflow chart provides the sequence and a brief description of operations without specifying transitions and process modes, while in the second case they are supplemented by a full description of some operations provided in other documents (for example, standard operation charts) [3]. Automated process design systems are used [4] to further reduce costs at the design stage. As a rule, those contain their own databases (guides, part drawings, equipment libraries, sets of standard processes) or use external databases. After automatic task-setting in the dialogue format, the required fabrication documentation (FD) is prepared.

In the existing form, none of the two approaches considered above provides a cardinal improvement when considering small-scale assembly of complex devices. This requires a new intellectual product which would allow to shatter a seemingly impregnable stronghold of the manufacturing cost of a small-scale assembly process itself. Doing so requires to go through all stages of the life cycle of a given product. To begin with, it is suggested to analyse the available alternatives and create a suitable model for the future process to be developed.

Investigation. Toy blocks as a process model

The history of construction kits dates back to 1880s, when future aeronautics pioneers Otto and Gustav Lilienthal came up with a set of miniature building blocks of three types (coloured bricks, briquettes, and roofing) for children. The Anchor stone block sets contained instructions following which a child could assemble a model of a building (Fig. 2, a). One of such sets, numbering 160 blocks, belonged to A. Einstein.

Nowadays, Lego construction sets based on hollow plastic bricks that snap together with cylindrical spikes and tubes are among the most popular options. The sets include many other parts: panels, cones, wheels, and gears. High accuracy of manufacturing (10 µm) of Lego parts allows to attach them to one another easily and reliably and to assemble models of cars, trains, buildings, and robots.

Flagship sets designed for 4–7-year-old children contain dozens of variously shaped parts, and the sets developed for 10–14-year-old children allow to assemble technically complex objects of a thousand or more parts (Fig. 3). When considering the process of their assembly from the manufacturing point of view, it can be noticed that the coefficients of operation assignment to children’s “workstations” roughly coincide with the standard values for RES production.

Similarly to the children’s construction set assembly, assembling devices within RES is a process of mechanical (or electrical, as far as electrical wiring is concerned) attachment of parts and radio components.

What makes children able to handle the tasks that require involvement of highly qualified specialists in “adult” manufacturing life?

The problem is that, having received a set of standard workflow charts (and even instruction cards), an unskilled performer finds himself utterly helpless and intimidated by a pile of instructions that are hard to understand.

For the purposes of solving this issue, visual aids were introduced to production flowcharts within the FD (drawings of parts with the numbering of all surfaces, sketches of operations, including the image of the tool to be used). Visual aids are provided separately in the form of sketch charts or are placed directly in the field of an instruction card in a designated place (Fig. 4, a).

Fig. 4. Fabrication documentation (FD):
a – instruction card (machining at automatic lathe) of pipe union fabrication process;
b – helicopter assembly instructions from Lego Technic 42052 set, sheet 36

The use of sketches facilitates the process of complex information perception but does not make any drastic changes primarily because of the ambivalent character of the solution: 2D blackand-white drawings represent a pale imprint of reality and are merely an addition to the formalized text.

Fundamentally, developers of brain-building construction sets do not build on the formal description of the world but appeal to children’s figurative, non-verbal thinking. Children as young as two years old easily perceive bright threedimensional images. They can assemble models of rather complex objects following the instructions in the exclusively pictorial format. A 10-year-old child provided with visual aids only (Fig. 4, b) can assemble a Lego helicopter model just for several hours, performing more than 300 complete mechanical operations.

The visual channel of information perception has the highest bandwidth for an adult, so we can expect that the operational description of the process with as many visual aids as possible would reduce the assembly time when compared to the traditional forms of process design. However, the ultimate effectiveness of such an approach is highly dependent on the cost of developing a Lego-like FD.

Development. In search for a tool kit

At the next stage, following the analysis and statement of the problem, it is necessary to develop tools and define the methodology of its solving. The case at hand refers to the tools and methods of developing FD of a new type.

The use of computer-aided design (CAD) systems for process development is limited by the individual character of the sequence of assembly, and hence of process diagrams, as well as by the lack of formalized descriptions for the most of the transitions in contrast to the fabrication processes of manufacturing. In addition, all process CAD systems are focused on issuing a production flowchart of a standardized format.

In order to prepare a set of Lego-like FD, it is necessary to understand how Lego instructions are created. Combining Lego elements allows to assemble a non-standard design structure and
even compile an instruction for its assembly. In the book [5] it is recommended to use a digital camera for this purpose. First of all, it is suggested to take pictures of all the parts needed for the assembly. Then each step in the process of installing and joining parts has to be photographed, i.e. it is necessary to take pictures of the assembly process operation by operation, including pictures of individual assemblies (assembly units) and of the structure as a whole. After that, the photos need to be imported in a text editor or a video editing software. However, the majority of images are created with the help of computeraided design software allowing to design the entire structure [5].

Modern CAD systems are a powerful tool for creating design documentation based on 3D modelling [6]. At the same time, the work performed by a design bureau team simulates the operation of personnel involved in the main production following the same stages of a life cycle. Initially, 3D models of elements are created based on sketches (work piece processing) or imported from databases (components purchasing), then 3D models of elements are created, then 3D assembly of assembly unit models (unit assembly) is performed, then the assembly of a 3D product structure as a whole (general assembly) takes place with the only difference consisting in the fact that CAD systems are used as a means of production instead of tools and process equipment used for the actual production.

The difference between a virtual assembly process and a real one is in designer’s ability to save the intermediate results (states of the material product) after each operation, therefore, these 3D models can become the basis for a new technology of describing fabrication processes hereinafter referred to as Lego-like technology. On the other hand, the sequence of virtual 3D assembly operations may differ from that prescribed by the fabrication process for creating a material product. In the given situation, one can disassemble the finished 3D model of the product into elements and reassemble it in accordance with the traditionally developed process (or simply hide unnecessary elements). Better yet, one can start designing the process and create design documentation at the same time as soon as the concept of a new device is ready.

3D process development and assembly performance

Upon finding a suitable tool and defining on how to use it, an attempt was made to develop the assembly process for an actual device by two methods.

The start of the development was the same for both options. The sequence of operations was traditional, as in the development of a standard process:

• developing a manufacturing workflow in the format of a structured hierarchical tree;
• composing a diagram of operations on the process workflow;
• selecting tools and equipment, defining process modes.

Then it is necessary to prepare two types of production flowcharts: standard instruction cards (v1.0) and Lego-like charts (v2.0) according to the designed mock-up. The standard CAD systems (Fig. 5) and 3D models from the electronic design documentation were used to create the new type of charts. Upon placing the 3D model of an assembly unit into the workspace, the developer set up the desired lighting and viewing angle, hid some parts, leaving only the ones designated at the beginning (or end) of the operation, and rendered the object. For a complete description of the operation, 3D models of the parts to be installed were added to the upper area of the chart with pointers to installation locations, along with lists of parts. The assembly workflow and Lego charts v2.0 of the main branch are shown in Fig. 6. Thus, the average time of v2.0 chart production was approximately 20 minutes per one Lego chart (just over half a minute per single elementary operation), which is comparable to the time of v1.0 instruction cards production by specialized CAD systems and much less than the time required for manual preparation of production flowcharts.

Fig. 5. Rittal light 4139.159 installation in cabinet TS8 Rittal 8865.500:
a – execution; b – 3D modelling

Fig. 6. Distribution cell fabrication process description:
a – assembly workflow; b – Lego-charts (v2.0) of the main line of the distribution cell assembly workflow

In order to verify the assumptions stated above and evaluate the effectiveness of the Lego technology, it was decided to hand over both types of documentation to medium-skilled assemblers and compare the results of their use.

Stunning results were observed: the average labour cost to assemble a cell using conventional instruction cards for a batch of 10 pieces was approximately 36 man-hours, while using Lego charts the cell assembly was performed in one two-shift working day. This can be partly explained by the use of parts with tolerances characteristic of assembly by the method of complete interchangeability (serial factory relays, circuit breakers, contactors, housing elements, etc.) and the use of compensators.

As a result of the first practical tests, the assemblers and military acceptance representatives expressed their wishes regarding the necessity of additional textual legend, demonstration of the tools used and many others, in view of which the process of detailed design of production Lego chart v2.1 started. The common field of a Lego instruction sheet with the 3D model of the product was preserved in the initial and final states. All the necessary attributes of a standard instruction card were added as well: textual legend, indications of the used tools, parts installation layouts, etc. (Fig. 7).

Fig. 7. Lego charts (v2.1):
a – power busbars installation; b – distribution cell installation

The missing pictures (photos, 3D models) of tools and process equipment (soldering stations, etc.) were pulled from suppliers’ sites or manufactured independently. As a result, a process model was prepared with aggregation of such types of information models as image-bearing (photos of tools, 3D models of assembly units, parts, and fasteners), mixed (part installation layouts, etc.) and alphanumeric (textual legend).

Lego charts v2.1 were used to assemble a more complex product: a switchgear cabinet (SC) with its process comprising approximately 2,600 elementary assembly operations, some of which needed to be adjusted, excluding the assembly of seven cells.

The SC assembly time by a highly-skilled assembler when using conventional instruction cards was 128 hours, or 2.95 minutes per single elementary operation. When using Lego charts, it took a medium-skilled assembler 80 hours to assemble (1.85 min/operation). The data on costs, including the process development with the use of the Lego-like technology, are summarized in Table 3.

Table 3

Manufacturing costs when using Lego-like technology

The table shows that the use of Lego-like technology for describing the assembly process pays off starting with the batch size of 1 pc. Operation time depends less on the batch size than when using traditional production flowcharts. Moreover, it is possible to predict the efficiency of Lego-like technology not only for single-part production. The dependence of labour costs per operation on the batch size as per results of distribution cell assembly is shown in Fig. 8 (solid curves show the result of approximation by the functions of y = b + ax^c form).

Fig. 8. Labour costs per single operation depending on the batch size

The analysis of the corresponding curves for assembly by medium- and high-skilled personnel when using traditional production flowcharts (red and purple curves) and by medium-skilled personnel when using Lego charts (blue curve) proves that the latter option is more effective at least up to the manufacturing volume of 100–150 pcs.

According to CALS (continuous acquisition and life-cycle support) strategy, the creation of digital process v2.x versions for tablets and industrial PCs, which can be installed directly on workstations or available servers, appears relevant (the currently implemented version is presented in Microsoft PowerPoint – Fig. 9, b). At the stages of the product life cycle application and modernisation, interactive electronic technical manuals (IETM) intensively implemented over the last 10–15 years appear to be similar intellectual products. The main task of IETM is to reduce equipment repair and maintenance time by providing information in the most convenient format. Such manuals include databases and electronic display systems.

Fig. 9. Viewer display:
a – SiberSafe S1000D IETM Viewer; b – Microsoft PowerPoint + Lego-ТП v2.1

One of the most popular standards in this area, originally developed for technical publications in aircraft engineering, is ASD S1000D used for data modules (component catalogues, descriptions of operating principles and maintenance and repair procedures) combined into a common database. Russian GOSTs have been also developed on its basis. Visual aids, textual information, and tables are displayed in the user area of the IETM window. As a rule, visual aids are executed in blackand-white vector graphics: assembly drawings and images in axonometric projection or in exploded view (Fig. 9, a) [7]. The standard allows adding images and 3D models, but this applies primarily to individual modules and databases of individual developers. General databases (including component catalogues) are not fit for it.

Black-and-white visuals somewhat reduce the effectiveness of the visual aids approach: the standard levels of reduction in maintenance and repair time are estimated at 25–30 %. However, it allows to make publications compatible and apply common databases without increasing the development time when using specialised software. When creating the following digital versions of processes on the basis of Lego-like technology, using similar modular structures with development of the necessary databases, preserving colour 3D models as the basis for visual aids, is believed to be the most promising path forward.

With further development, Lego-like technologies can be used in the assembly procedures for antenna and SHF devices. Figure 10 shows an example of a 3D model for an Х-band active phased antenna array (APAR) transceiver module (TM). APAR normally contains hundreds and even thousands of transceiver modules, therefore, increasing the productivity of TM assembly technologies is highly relevant starting from the stage of prototype production and for series production.

Fig. 10. 3D model of an X-band transceiver module:
1 – cap; 2, 10 – covers; 3, 8 – fins; 4 – housing; 5 – power amplifier chip assembly; 6 – receiving amplifier chip assembly; 7 – sending amplifier chip assembly; 9 – joint board; 11 – routing board; 12 – 12 VMA adapter; 13 – glass-to-metal seal; 14 – collet

Conclusion

A new technology was developed for describing a process of small-scale production (Lego-like technology) based on 3D computer modelling and Lego approach to designing instructions for assembling children’s construction sets.

As a result of the first practical testing of Lego-like technology, the possibility of a drastic increase in labour productivity was confirmed at least with regard to the assembly of power distribution devices within RES at relatively low labour costs for process development. The achieved results demonstrate undeniable prospects of using Lego-like technology in process development. Further development of the Lego-like technology may proceed in the following directions:

• improving the format of production Lego-charts;
• organizing simultaneous development of design and fabrication documentation;
• creation of tool and equipment databases;
• integration of Lego approach into modern process CAD systems;
• creation of digital process versions v2.x for tablets and industrial PCs, which can be installed at workstations of highly concentrated production.