A recent study was conducted by Statista in the US for mapping the inclination of automotive customers towards the key buying factors. Image below shows that safety & fuel efficiency are the winners but significant numbers are with High Quality & Design as well.
For Indian automotive customers the scenario is almost similar nowadays, the buying parameters list has increased recently and the new addition is interior and exterior aesthetics of the vehicle. Be it any category of vehicles, the OEM’s concern for the quality of trims and fit & finish has increased exponentially.
While design & development of automotive trims all of the parameters from Statista should be evaluated priority wise and design channels should be set in order such that the final thing fits best in all the parameters and the outcome is the best of all possible cases. This series of blogs (Automotive Trim Design 1/2/3) will focus on the key design considerations in line with the buying parameters and their significant impact on the ease of product development for Indian OEMs. The example used in this blog are based on the projects we have completed for various clients in the recent past.
Following is the general workflow that is followed for the design and development of interior and exterior trims of automobiles in OEMs.
The styling and design teams at automotive OEM’s always walk an extra mile to make the best looking interior and exterior trims. But, when it comes to engineering for feasibility study, there are various constraints that are not well thought and analyzed due to time constraints. As a result, the best-looking styling gets compromised in the production vehicle. Above shown workflow the initial activity of styling and Class A Surface modelling is done by the client and the rest of the activity is done by ASI with client representatives at every stage of development.
To support OEM’s overcome such challenge of delivering competitive and superlative quality trims, we have come up with a methodical approach that focuses on the major selling points of the vehicle. The approach is explained through following 3 blogs:
Blog-1: Class A Surface engineering feasibility check & feedback. (You are reading this blog) (refer block-1 from above image)
Blog-2: Matching concept design (Cut-lines and type of fit philosophy) in detail.(refer block-2 from above image)
Blog-3: Master sections, Detailed Design considerations, B-Surface Modelling, Supplier Feedback & drawing release(refer block-3 from above image)
Class A Surface feasibility check
The Class A surface provided by the OEM is passed through various engineering constraint channels defined for a given part. An example of A-Pillar trim is considered and all the engineering considerations are explained one after another.
General Flow Image
For instance, an A-Pillar interior trim class A Surface will go through following channels and checked for worst case scenario in terms of weather conditions and manufacturing tolerances:
1. Homologation Check:
a. ECE-R21 is to be referred to comply with interior fittings regulation, specifically for sharp edges (minimum corner radius), Head injury criteria and projection rules. (Refer image below)
b. AIS-021 is to be referred for A-Pillar obstruction angle which should be less than 6°. The A-Surface should not obstruct the vision which lies generally between the ceramic lining for windshield and door glass beading. (Refer image below)
For all these homologation checks, basic tools & macros are used to expedite the repeated process.
2. Surrounding parts check:
a. Windshield: Class A Surface needs to be non-interfering with the windshield and edge of the trim on windshield side should be positioned from the glass surface and ceramic line at uniform distance.
b. Body Panel: Considering the space for mounting the Class A surface position should be at minimum distance to accommodate the mounting philosophy decided.
c. Electrical: Any harness that is behind the A-Pillar needs to be offset and interference to be checked, the values of clearances need to be confirmed by the client as it is purely based on manufacturing tolerances.
d. Instrument Panel: Basic IP & A-Pillar integration needs to be studied, cutline and mounting method to be check with current A-Surface
e. Roof Trim/lining: Generally, the Class A Surface of Roof lining & A-Pillar is made together so the chances of a wrong A-Pillar surface there is less however, it has to be checked for matching and the mounting philosophy.
f. Door Flange Beading: Based on the concept of Class A Surface above or below the beading the lip of the beading and surface near that area to be checked for worst case scenario.
g. Curtain Airbag: In case of top variant model where curtain airbag is necessary, enough space requirement is to be checked in co-ordination with BIW & airbag design team.
In case of access to connectors/harness/speakers etc. behind the A-Pillar Trim, the part should be easy to remove and reassemble. Basic servicing philosophy should be thought off with Class A Surface and few sections, this will be done in detail during Class B Surface modelling, however in case of any abnormality in the Class A Surface can be pointed out at this stage.
4. Assembly Locus:
Considering the high volumes OEM’s aim at, the time required by an operator to fit the part to the vehicle on an assembly line should be minimum. Also, the assembly steps should be easy to understand and follow. To do the same, considering the flexibility of the part, assembly locus is defined and the steps are checked. In case of an A-Pillar the positioning of the part in Instrument panel has to be studied in detail.
5. Tool Accessibility:
In case of any screw/bolt/clip that is used to fasten the part on the vehicle, tool required to mount it should be checked on the CAD for the reachability and operational hinderances, if any.
The manufacturing process & material needs to be finalized with the client and feasibility is to be checked accordingly, generally in case of passenger cars the PP (Poly Propylene) granules will be melted and injection molded in a die to make A-Pillar Trims, however in Buses, vacuum forming or FRP lay-up can be used.
Based on the decided thing, feasibility for draft angle, unnecessary undercuts are to be checked. Parting line, slider lifter direction needs to be studied in detail. Detailed considerations for avoiding plastic defects need to be studied during B-Surface & Master section stage.
7. Part Durability:
The part should be durable in all weather conditions, for that basic thermodynamic calculations are done to identify the maximum elongation & contraction of the part during heat cycle and cold cycle respectively. Mounting method should be decided to control the dimensional stability of the part.
8. Part Handling:
Material handling teams at all OEM’s spend huge amount of time in designing trolleys and effective material management to ensure minimum damage of parts arriving on assembly line. While designing the part, such considerations of having non-abrupt features and sharp edge on corners etc. help in better handling of the parts.
9. Customer Perception:
Nowadays, customers perceive the strength of the vehicle by looking at trims and sometimes pressing them at locations. In order to enhance that perception of buying a stronger vehicle, finger press test is conducted at easily accessible locations to ensure it feels strong. The basic level 2D CAE can be conducted to check the local strength of the part. Based on this, the thickness profile of the part and ribs arrangements can be decided.
The outcome of passing the Class A Surface through all these channels is the feedback drawing which includes all the details of why and how the Class A Surface modification is necessary. ASI engineering team discusses the feedback and explains the styling team about the constraints.
Similar activity is designed for other trims as well for which there might be many other design considerations will be in effect.
Once the Class A Surface is updated it is rechecked by the engineering team for all constraints and passed on for the detailed design that will be discussed in the 3rd Blog.