What Aerospace and Defense OEMs Need to Know
While they read similarly, build-to-spec and build-to-print manufacturing are two very different engagement models that serve very different purposes – and OEMs need to understand the implications each carries relative to the manufacturing process.
OEMs and manufacturers are allocated specific ownership and responsibility based on whether they are engaged in a build-to-spec (BTS) or build-to-print (BTP) program.
Parameters include who has control over design, who owns intellectual property, who assumes risk, what costs are included, and other potential program outcomes.
In this article, we explain each engagement model, and the role it plays in manufacturing, so OEMs and manufacturers can better navigate complex aerospace and defense programs.
What is Build-to-Spec Manufacturing?
A build-to-spec manufacturing model shifts a portion of the design responsibility from the OEM to the manufacturer. An OEM may prefer a BTS model for a number of reasons:
- They want to leverage the supplier’s engineering expertise
- The part needs to be optimized for specifications like tolerances, weight, cost, or manufacturability
- There is flexibility in how performance objectives can be achieved
- Engineering collaboration will help increase speed-to-market
To execute a part program from design and engineering through production, the manufacturer needs the OEM to provide performance requirements, regulatory and compliance standards, environmental constraints, and any other design considerations.
Now that the OEM has specified what the part needs to do, the supplier has the freedom to define how the part will do it. However, collaboration between the OEM and manufacturer remains important as each party assumes some accountability for part design and production.
A build-to-spec approach may not work well if product designs aren’t fully developed, documentation is incomplete, or high-level engineering expertise is required from the manufacturer.
What is Build-to-Print Manufacturing?
Dissimilarly from a build-to-spec engagement, under a build-to-print model, the OEM supplies complete engineering documentation to the manufacturer. An OEM may favor a BTP model if:
- Their designs are highly specialized or proprietary
- The designed part is one component of a larger validated and qualified platform
- They are concerned with limiting external engineering influence
- There is tight control over certification requirements
The OEM is responsible for supplying any supporting documentation about the part; detailed drawings, CAD models, materials and finishing specifications, and quality control standards. The supplier cannot alter geometries, materials, or tolerances without formal approval from the OEM, and the OEM maintains total accountability for design performance.
A build-to-print approach may not work well if drawings are incomplete, poorly done, overly constrained, or not optimized for manufacturability.
The Implications of Build-to-Print and Build-to-Spec Models on Manufacturing
Let’s break down the ownership and characteristics of each engagement model:
| Build-to-Print | Build-to-Spec | |
|---|---|---|
| Design Authority | 100% OEM | 100% supplier but ultimately depends on contract |
| Intellectual Property Ownership | 100% OEM | Negotiated or shared |
| Engineering Input / Direction | 100% OEM | Collaborative between OEM and supplier |
| Risk Accountability | OEM assumes design risk while the supplier assumes production risk | Typically falls more on supplier but depends on contract terms |
| Flexibility | Low; documentation dictates execution | High; supplier has greater design discretion |
| Cost Structure | Predictable, assuming prints are mature and stable | Less predictable; may include engineering development costs |
| Innovation Opportunity | Limited | Higher, especially when supplier expertise adds value |
Selecting Build-to-Print or Build-to-Spec for Aerospace Programs
A build-to-print or build-to-spec model ensures critical requirements are met throughout the part program. But how do you know which type of engagement to pursue?
Choose build-to-print when:
- The design is mature and fully qualified
- IP sensitivity is high
- Configuration control is critical
- The OEM is able to assume engineering responsibility
Under a build-to-print manufacturing model, compliance documentation and configuration control is straightforward, and the OEM can retain control over any proprietary data.
Plus, BTP programs typically provide lower upfront costs and fewer unexpected costs due to clearly-defined documentation.
Choose build-to-spec when:
- The OEM wants manufacturing-driven design optimization
- Engineering resources are limited
- There is a need for specific weight, cost, or material improvements
- Collaboration is needed for a competitive advantage
Under a build-to-spec model, OEMs provide more information up front but enjoy a more collaborative approach with clearly-defined ownership and responsibility across the manufacturing program.
A build-to-spec model may require a higher upfront engineering investment, but there are long-term cost efficiencies gained through part optimizations like weight reduction, improved material utilization, and reduced machining complexity. The determining factor is whether cost or design control is the OEM’s higher priority.
BTS Vs. BTP: The Best of Both Worlds
Given the varying parameters of each engagement approach, it’s not surprising that many aerospace programs leverage both build-to-spec and build-to-print manufacturing models.
For example, an OEM may have a highly specialized design and favor a built-to-print model to ensure the manufacturer follows the complete engineering documentation. However, the OEM may also want recommendations from the supplier for manufacturability improvements, thereby shifting to a build-to-spec model that gives more flexibility to the manufacturer to apply their engineering expertise.
Following build-to-spec, build-to-print, or both entirely depends on the program requirements and identifying the best approach to achieve them.
At Primus, we support both engagement models and work with our OEMs to execute based on their needs and the needs of the program. Regardless of approach, we adhere to a best-practice approach:
- Full transparency
- Thorough documentation and traceability
- Compliance-aligned quality systems
- Collaboration on designing for manufacturability
- Strict adherence to the OEM’s defined engineering authority
While we can collaborate to meet performance criteria or needs (build-to-spec) or execute a program precisely to documented specifications (build-to-print), we can promise precision machining that delivers mission-critical quality.
