Laser Welding Plastic Watch Crystal to Case

Resolve Bottlenecks,
Find Innovative SolutionsGenerate Solutions

Solution Overview

Problem

Existing methods for attaching a plastic watch crystal to a plastic watch case, such as bonding and ultrasonic welding, often result in mechanical and thermal stress issues, leading to spacer aggregation and black spots in liquid crystal display devices, and disrupt production flow due to polymerization time requirements.

Innovation Solution

Laser welding is used to attach the plastic watch crystal to the watch case, avoiding mechanical and thermal stress effects on the digital display device and allowing for immediate assembly without polymerization delays.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If ultrasonic welding is used to attach the crystal to the case, then the assembly is watertight and durable, but the mechanical vibrations and temperature rise cause spacer aggregation and black spots in the liquid crystal display

Engineering Contradiction:

Improvewatertight and durable assemblyVSAvoidspacer aggregation and black spots in display

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The patent replaces the ultrasonic welding process (mechanical vibration-based) with laser welding (thermal energy-based). The laser beam welds the crystal to the case without causing the mechanical vibrations that lead to spacer aggregation, while still achieving a watertight and durable assembly through controlled thermal melting and bonding.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent changes the welding parameters by switching from high-frequency mechanical vibrations (ultrasonic) to controlled thermal energy input (laser). This parameter change eliminates the harmful mechanical effects on the liquid crystal spacers while maintaining the bonding effectiveness through temperature-controlled melting and fusion of the materials.

Inventive Principle:

Principle #35Parameter changes

2Object-affected harmful factors

If bonding techniques are used to attach the crystal, then no mechanical or thermal stresses are induced, but the assembly requires polymerization time causing production interruptions

Engineering Contradiction:

Improveno mechanical or thermal stressesVSAvoidproduction flow continuity

Core Design Contradiction:

Object-affected harmful factorsVSProductivity

Solution Approach 1:

The patent replaces chemical bonding (requiring polymerization time) with laser welding (physical bonding through melting). This substitution eliminates the waiting period for chemical polymerization while still avoiding the harmful mechanical vibrations of ultrasonic welding, achieving both stress-free assembly and immediate production continuity.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent enables continuous production flow by using laser welding, which provides immediate bonding upon completion of the welding process. Unlike bonding techniques that require a polymerization waiting period, laser welding achieves full bonding strength instantly, allowing the production line to proceed without interruptions or delays.

Inventive Principle:

Principle #20Continuity of useful action

3Productivity

If laser welding is used to attach the crystal, then immediate assembly is possible without polymerization time, but high temperatures may affect the digital display device

Engineering Contradiction:

Improveinstant assembly and continuous productionVSAvoidthermal effects on digital display

Core Design Contradiction:

ProductivityVSObject-affected harmful factors

Solution Approach 1:

The patent applies local quality control by concentrating the laser energy only at the bonding interface between the crystal and the case, rather than heating the entire assembly. This localized heating approach enables instant assembly through rapid bonding at the joint while preventing thermal damage to the temperature-sensitive digital display device mounted on the crystal.

Inventive Principle:

Principle #3Local quality

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 laser welding method provides a watertight, durable, and stress-free attachment that maintains the mechanical and optical properties of the liquid crystal display, enabling continuous production flow and enhanced resistance to connector forces.

Implementation Method 1

it consists in welding the crystal to the middle part by means of a laser beam

Methodology Applied

Scientific EffectLaser welding: Laser Beam Welding

Implementation Method 2

the ultrasonic welding technique makes it possible to attach the crystal to the caseband of the watch

Methodology Applied

Scientific EffectUltrasonic welding: Ultrasonic Vibration

Data Source

PatentEP2584413B1Method for attaching a glass to a middle of a watch case

Publication Date: 2014.08.13 ETA SA MFG HORLOGERE SUISSE

Figure 1

AI summary

Method of fixing a watch crystal (4) made of plastic to a case (2), also made of plastic, which together with the crystal (4) defines a watch case (1), this watch crystal (4) comprising an upper face (6) directed towards the user and an lower face (8) opposite the upper face (6), a digital display device (12) being glued to the lower face of the crystal (4), this method being characterized in that it consists of welding the assembly formed by the crystal (4) and the digital display device (12) to the case (2) by means of a laser beam.