Jürgen Kunz – Director Product Development – Oracle ORACLE Deutschland B.V. & Co. KG

Introduction

In a difficult economic environment, it is important for companies to understand the customer requirements in detail and to address them in their products. Customer specific products, however, usually cause increased costs. Variant management helps to find the best combination of standard components and custom components which balances customer’s product requirements and product costs.

Depending on the type of product, different approaches to variant management will be applied. For example the automotive product “car” or electronic/high-tech products like a “computer”, with a pre-defined set of options to be combined in the individual configuration (so called “Assembled to Order” products), require a different approach to products in heavy machinery, which are (at least partially) engineered in a customer specific way (so-called “Engineered-to Order” products).

This article discusses different approaches to variant management. Starting with the simple Bill of Material (BOM), this article presents three different approaches to variant management, which are provided by Agile PLM.

Single level BOM and Variant BOM

The single level BOM is the basic form of the BOM. The product structure is defined using assemblies and single parts. A particular product is thus represented by a fixed product structure. As soon as you have to manage product variants, the single level BOM is no longer sufficient. A variant BOM will be needed to manage product variants. The variant BOM is sometimes referred to as 150% BOM, since a variant BOM contains more parts and assemblies than actually needed to assemble the (final) product – just 150% of the parts

You can evolve the variant BOM from the single level BOM by replacing single nodes with a placeholder node. The placeholder in this case represents the possible variants of a part or assembly. Product structure nodes, which are part of any product, are so-called “Must-Have” parts. “Optional” parts can be omitted in the final product. Additional attributes allow limiting the quantity of parts/assemblies which can be assigned at a certain position in the Variant BOM. Figure 1 shows the variant BOM of Agile PLM.

Figure 1 Variant BOM in Agile PLM

During the instantiation of the Variant BOM, the placeholders get replaced by specific variants of the parts and assemblies. The selection of the desired or appropriate variants is either done step by step by the user or by applying pre-defined configuration rules. As a result of the instantiation, an independent BOM will be created (Figure 2).

Figure 2 Instantiated BOM in Agile PLM

This kind of Variant BOM  can be used for „Assembled –To-Order“ type products as well as for „Engineered-to-Order“-type products. In case of “Assembled –To-Order” type products, typically the instantiation is done automatically with pre-defined configuration rules. For „Engineered- to-Order“-type products at least part of the product is selected manually to make use of customized parts/assemblies, that have been engineered according to the specific custom requirements.

Template BOM

The Template BOM is used for „Engineered-to-Order“-type products. It is another type of variant BOM.

The engineer works in a flexible environment which allows him to build the most creative solutions. At the same time the engineer shall be guided to re-use existing solutions and it shall be assured that product variants of the same product family share the same base structure.

The template BOM defines the basic structure of products belonging to the same product family. Let’s take a gearbox as an example. The customer specific configuration of the gearbox is influenced by several parameters (e.g. rpm range, transmitted torque), which are defined in the customer’s requirement document. 

Figure 3 shows part of a Template BOM (yellow) and its relation to the product family hierarchy (blue). 

Figure 3 Template BOM

Every component of the Template BOM has links to the variants that have been engineeried so far for the component (depending on the level in the Template BOM, they are product variants, Assembly Variant or single part variants). This library of solutions, the so-called solution space, can be used by the engineers to build new product variants. In the best case, the engineer selects an existing solution variant, such as the gearbox shown in figure 3. When the existing variants do not fulfill the specific requirements, a new variant will be engineered. This new variant must be compliant with the given Template BOM. If we look at the gearbox in figure 3  it must consist of a transmission housing, a Connecting Plate, a set of Gears and a Planetary transmission – pre-assumed that all components are must have components. The new variant will enhance the solution space and is automatically available for re-use in future variants.

The result of the instantiation of the Template BOM is a stand-alone BOM which represents the customer specific product variant.

Modular BOM

The concept of the modular BOM was invented in the automotive industry. Passenger cars are so-called „Assembled-to-Order“-products. The customer first selects the specific equipment of the car (so-called specifications) – for instance engine, audio equipment, rims, color. Based on this information the required parts will be determined and the customer specific car will be assembled.

Certain combinations of specification are not available for the customer, because they are not feasible from technical perspective (e.g. a convertible with sun roof) or because the combination will not be offered for marketing reasons (e.g. steel rims with a sports line car).

The modular BOM (yellow structure in figure 4) is defined in the context of a specific product family (in the sample it is product family „Speedstar“). It is the same modular BOM for the different types of cars of the product family (e.g. sedan, station wagon). The assembly or single parts of the car (blue nodes in figure 4) are assigned at the leaf level of the modular BOM. The assignment of assembly and parts to the modular BOM is enriched with a configuration rule (purple elements in figure 4). The configuration rule defines the conditions to use a specific assembly or single part. The configuration rule is valid in the context of a type of car (green elements in figure 4). Color specific parts are assigned to the color independent parts via additional configuration rules (grey elements in figure 4).

The configuration rules use Boolean operators to connect the specifications. Additional consistency rules (constraints) may be used to define invalid combinations of specification (so-called exclusions). Furthermore consistency rules may be used to add specifications to the set of specifications. For instance it is important that a car with diesel engine always is build using the high capacity battery. 

Figure 4 Modular BOM

The calculation of the car configuration consists of several steps. First the consistency rules (constraints) are applied. Resulting from that specification might be added automatically. The second step will determine the assemblies and single parts for the complete structure of the modular BOM, by evaluating the configuration rules in the context of the current type of car. The evaluation of the rules for one component in the modular BOM might result in several rules being fulfilled. In this case the most specific rule (typically the longest rule) will win. Thanks to this approach, it is possible to add a specific variant to the modular BOM without the need to change any other configuration rules.  As a result the whole set of configuration rules is easy to maintain. Finally the color specific assemblies respective parts will be determined and the configuration is completed.

Figure 5 Calculated Car Configuration

The result of the car configuration is shown in figure 5. It shows the list of assemblies respective single parts (blue components in figure 5), which are required to build the customer specific car.

Summary

There are different approaches to variant management. Three different approaches have been presented in this article. At the end of the day, it is the type of the product which decides about the best approach. 

For „Assembled to Order“-type products it is very likely that you can define the configuration rules and calculate the product variant automatically. Products of type „Engineered-to-Order“ ,however, need to be engineered. Nevertheless in the majority of cases, part of the product structure can be generated automatically in a similar way to „Assembled to Order“-tape products. 

That said it is important first to analyze the product portfolio, in order to define the best approach to variant management.