Medical Device Screw-Bushing Assembly to Prevent Sink Marks
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Solution Overview
Problem
Existing medical device components, particularly those made of plastic, face challenges with sink marks and complex assembly due to traditional screw connections, which affect mechanical properties and visual appearance.
Innovation Solution
A component arrangement featuring a bushing axially supported between a screw head and a component face, with a slimmer screw boss design and optional locking mechanisms, allowing for simplified manufacturing and assembly, improved force transmission, and prevention of sink marks.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a traditional screw connection is used in plastic components, then the mechanical fastening is achieved, but sink marks occur on the component surface affecting visual appearance and mechanical properties
Solution Approach 1:
A bushing is introduced as an intermediary element between the screw head and the plastic component. The bushing distributes the clamping force over a larger area, preventing localized stress concentration that causes sink marks. The bushing acts as a force distribution mediator while maintaining the mechanical fastening function.
Solution Approach 2:
The fastening system is segmented into multiple functional elements: the screw provides threading engagement, the bushing provides force distribution, and the screw head provides clamping force. This segmentation allows each element to be optimized for its specific function, with the bushing specifically addressing the sink mark problem.
2Strength
If a standard thickness screw boss shaft is used, then sufficient mechanical strength is achieved, but the component design becomes more complex and manufacturing less efficient
Solution Approach 1:
The bushing material parameters (density, compressibility, hardness) are selected to optimize force distribution. By changing the material parameters of the intermediary element, the system achieves effective force distribution without increasing the boss shaft dimensions, simplifying manufacturing while maintaining strength.
3Loss of substance
If the screw shaft is made thinner to reduce material usage, then material waste is reduced, but the mechanical properties of the screw connection are compromised
Solution Approach 1:
The bushing serves as a mediator that compensates for the reduced shaft thickness. It provides the necessary structural support and force distribution that would otherwise require a thicker shaft, enabling material reduction without compromising connection strength.
4Manufacturing precision
If a bushing is added to the screw connection system, then force distribution is improved and sink marks prevented, but the number of components increases
Solution Approach 1:
The bushing is designed to perform multiple functions simultaneously: force distribution, sink mark prevention, and structural support. This multi-functionality justifies the additional component by consolidating several protective and structural roles into a single element.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution enables a slimmer design with enhanced mechanical properties, simplified assembly, and reduced material waste, while preventing sink marks and assembly errors, thus improving the manufacturing efficiency and visual quality of plastic components.
Implementation Method 1
The bushing serves as a spacer and force transmission element... the screw head exerts axial pressure on the bushing, which in turn is axially supported on the front face of the first component
Implementation Method 2
The screw thread forms its own mating thread when screwed into the boss shaft, specifically by cutting and/or grooving
Implementation Method 3
an interference fit is formed between the inner diameter of the bushing and the outer diameter of the screw shank
Data Source
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AI summary
The invention relates to a component arrangement for a medical device, in particular a dialysis machine, comprising a first component with a front, a back and a recess extending between the front and the back, a second component comprising a screw boss with a longitudinally extended boss shaft and a bore, wherein the second component is arranged at the back of the first component and the boss shaft projects axially through the recess over the front of the first component, a bushing which is axially pushed onto the first component via an end face projecting through the recess and is axially supported on the front of the first component, and a screw shaft having a thread and a screw head, wherein the screw shaft is screwed into the bore and the screw head is axially supported on the bushing, whereby the first component is screwed to the second component.